This is a known MS Win 10/11 scheme not just for Dell but HP and lenovo and all other major PC makers. 

What you could try is disable UEFI firmware update capsule in bios.  Whether or not this is 100% effective there is various user report.

In addition to redxps630's advice, if a new BIOS update is installed, UEFI Firmware Capsule Updates will be reenabled by default. To prevent future BIOS updates installed by Windows Update, UEFI Firmware Capsule Updates will need to be disabled again.

Hope this helps.

Disabling UEFI capsule updates can be effective ... or not. Microsoft/Windows can choose to ignore that setting.

Uninstalling SupportAssist would be wise.  The AI is reported to have superuser admin privilege which may force update bios despite user attempt to block it in bios.  SA is really meant for mainstream common users who are not keenly interested in managing pc on admin level and who would feel more comfortable delegating control to ostensibly safe MS-Dell alliance program (i.e. auto update).

To disable firmware updates through Windows Group Policy

1. Press the Windows key + R keyboard shortcut to open the Run command.
2. Type gpedit.msc and click OK to open the Local Group Policy Editor.
3. Browse the following path: Computer Configuration > Administrative Templates > Windows Components > Windows Update > Manage updates offered from Windows Update.
4. On the right side, double-click the Do not include drivers with Windows Update policy.
5. Select the Enabled option.
6. Click Apply and then OK

Hi @Robert Houston :

I have turned off Windows driver and BIOS firmware in the Local Group Policy Editor (gpedit.msc) of my Win 10 Pro v22H2 laptop as JamieLinux suggested <above> but that workaround isn't an option for you because your Win 11 Home OS does not have a Local Group Policy Editor.

I uninstalled SupportAssist v3.x from my Inspiron 5584 because I found that SupportAssist was too buggy, consumed too many system resources, and the "system optimization" scans (Clean Files / Tune Performance / Optimize Network) were too aggressive and had the potential to do more harm than good - see my 12-Jul-2021 comment in ex-jedi's Prevent Automatic Recycle Bin Emptying.  If you want to continue using SupportAssist I would strongly advise that you disable all automatic background updates checks and optimization scans at Options (gear icon) | Settings | Automate Scans and Optimizations | Set Your System to Automatically Run Scans and Performance Optimization as shown in the image below and just run "Get Drivers & Downloads" and "Scan Hardware" tasks manually from the Home tab of SupportAssist.

I now use Dell Update for Windows Universal v5.x to check for available Dell software and driver updates because this utility this software does not run in the background and automatically scan for updates (i.e., it must be launched manually), and any available updates it detects can be reviewed and declined (unchecked) to prevent installation.  The image below I captured in Aug 2022 shows I used Dell Update for Windows Universal to self-update to a newer version of this utility but declined updates for my BIOS firmware (highlighted in red) and Realtek Memory Card Reader driver.

...  Would uninstalling Support Assist and Dell Update be effective? I could then just go to the Dell site and find wanted updates ....

Just note that the blue Check for Updates button on your XPS 8950 support page at https://www.dell.com/support/home/en-us/product-support/product/xps-8950-desktop/drivers requires SupportAssist to be installed and will simply prompt you to reinstall SupportAssist if it is missing from your system.

However, if SupportAssist is uninstalled you can still click the This Device tab shown below and enter your unique Service Tag when prompted and this should display a filtered list of recommended updates that match your system components.

If you do not see the full list of available updates on your XPS 8950 support page after SupportAssist is uninstalled then see the workaround suggested by garioch7 in my Oct 2023 topic Recommended Updates (View List) Not Displayed on Inspiron 15 5584 Support Page.

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ASIDE: Be warned that many users in this forum advise against allowing utilities like SupportAssist v3.x and/or Dell Update v5.x to install BIOS updates just in case the update fails to run to completion and prevents you from booting up your system. See my 12-Sep-2023 post in bear-o's SupportAssist 3.10.4 Unexpected Issue about alternate (and safer) ways to update your BIOS.

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Dell Inspiron 5584 * 64-bit Win 10 Pro v22H2 build 19045.3803 * Firefox v121.0.0 * Microsoft Defender v4.18.23110.3-1.1.23110.2 * Malwarebytes Premium v4.6.6.294-1.0.2201 * Macrium Reflect Free v8.0.7783 * Dell Update for Windows Universal v5.1.0 * My Dell v2.2.6.0 * Fusion Service v2.2.14.0

You can add back the Group Policy Editor into any Home Edition of Windows.  Just follow the steps here.

How To Enable Group Policy Editor (Gpedit.msc) In Windows 11 Home (itechtics.com)

I have a XPS 8950 with Windows 11 Home. A few days ago, I checked for updates using Dell Update and found that a BIOS update had been downloaded and installed and I needed to restart...

Hi @Robert Houston :

If it was Windows Update, and not one of your Dell utilities, that automatically delivered your BIOS update then it should be listed somewhere in your Windows Update history (e.g., as a firmware update listed under "Other Updates").  I don't have a Win 11 OS, but according to the 01-Oct-2023 How-To Geeks article How to Update Drivers on Windows 11 most (but not all) driver updates are offered as optional updates at Windows Update | Advanced Options | Optional Updates and won't be installed unless you manually select them for installation. 

The 10-Nov-2022 MiniTool article How to Enable/Disable Automatic Driver Updates in Windows 11 notes that you can also change the Device Installation Settings in your Advanced System Settings [open a Run dialog box (Windows key + R) and enter sysdm.cpl] to prevent automatic driver updates by selecting "No (your device might not work as expected)", but I'm not certain this would also disable BIOS firmware updates.

I'm not sure why Dell Update for Windows Universal v5.x would have warned you to re-boot to finish a BIOS update if that update was delivered by Windows Update, but I know many Win 10 / Win 11 Home users who use a third-party utility call WUMgr to select which updates recommended by Windows Update are installed on their system.  See the 30-Aug-2022 itechtics.com article How To Manage Windows Updates Using WuMgr and geekdom's 06-Dec-2020 Guide to Using WuMgr for Windows 10 Updates (which is also valid for Windows 11) in the AskWoody.com forum.
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Dell Inspiron 5584 * 64-bit Win 10 Pro v22H2 build 19045.3803 * Firefox v121.0.0 * Microsoft Defender v4.18.23110.3-1.1.23110.2 * Malwarebytes Premium v4.6.6.294-1.0.2201 * Macrium Reflect Free v8.0.7783 * Dell Update for Windows Universal v5.1.0 * My Dell v2.2.6.0 * Fusion Service v2.2.14.0

@JamieLinux​ this doesnt really work. I did this in September, and it worked until Support Assist was updated last month, and now it ran a firmware update DESPITE having UEFI Capusle turned off in bios.

Deleting Support Assist is probably the only surefire way after doing the gpedit route.

I just can’t get this to stop repeating I have completely disabled automatic updates altogether in my system, then I entered bios and unchecked UEFI updates and now I’m just at a loss I have been working on this system now over an hour. Please help fix this issue I just want it to stop!!