TPM Trusted platform module

Do a search on the system for powershell, and open as administrator.  Type

get-tpm

The first line will tell you whether there's a TPM present.

It say false for Inspiron 3558.

How do I add TPM 2.0 to be compatible for Windows 11?

If there's no TPM, you can't add one.  However, you should be able enable Intel platform trust technology.  That said, bear in mind that Microsoft is ONLY supporting 11 on 8th generation and newer CPUs -- yours is older -- so you may find more obstacles.

https://www.dell.com/support/kbdoc/en-us/000181412/intel-platform-trust-technology-ptt

The system has a 5th Generation Intel Processor. There is no TPM 2.0, as this technology was introduced with 6th Generation Skylake Processors and newer.

I am enrolled to Windows Insider. So I usually get insider updates for Windows 10. The latest update which I received is Windows 11 and it is running great with no issues. I am using Inspiron 3558. 5th Gen i3 Processor. My laptop has no TPM and I did no changes to settings other than accepting the Windows 11 upgrade.

Keep in mind that after the release of Windows 11 you will receive no further updates and will have to reinstall Windows 10 as per this MS web page.

"Once Windows 11 is generally available, these PCs will be opted out of flighting and will not be able to receive future Windows 11 Insider Preview builds. These PCs must clean install back to Windows 10 with the media (ISOs) that we provide and can then join the Release Preview Channel to preview Windows 10 updates."