Can't enable TRIM on my Dell XPS 13 L322X SSD?

The "Access is denied" error is because you didn't start Command Prompt with elevated privileges, i.e. you need to right-click it and select "Run as administrator".  When you do that, the Command Prompt title bar will say "Administrator: Command Prompt" rather than just "Command Prompt".  However, the query command you ran first indicates that the setting you're trying to set to 0 is already set to 0, so setting it to 0 again won't change anything.  TRIM is already enabled.  The double negative wording makes it a bit confusing, but the setting is called "DisableDeleteNotify".  When that setting is disabled, it means that delete notifications are enabled, which means TRIM is on.

I ran Command Prompt as "Run as administrator" and got this:

So I'm good then?

@william66, unfortunately images are initially only visible to the person who uploaded them and to Dell moderators until they get "approved" for broader viewing, so I can't yet see the new image you posted, but as I already explained above, you were good even before you did anything because TRIM was already enabled.  There was absolutely no need to run a command to set an option the way the system clearly indicated it was already set.

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@jphughan wrote:

@william66, unfortunately images are initially only visible to the person who uploaded them and to Dell moderators until they get "approved" for broader viewing, so I can't yet see the new image you posted,

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So I'm the only one that could see the image/screenshot I posted??? That **bleep**. Just how long does it take for them to look at a photo???

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@william66 wrote:

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@jphughan wrote:

@william66, unfortunately images are initially only visible to the person who uploaded them and to Dell moderators until they get "approved" for broader viewing, so I can't yet see the new image you posted,

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So I'm the only one that could see the image/screenshot I posted??? That **bleep**. Just how long does it take for them to look at a photo???

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It's visible now.  And yes, it confirms that you successfully set DisableDeleteNotify to 0, which was how it was already set.  So you're good, just as you already were.