Impossible to use your own screensaver on the lock screen?

Like, if I lock my computer now, the screen will just eventually go black/turn off, it doesn't play the screensaver.

Yeah, that behavior is annoying, but there is a registry change that will resolve that for. Unfortunately, I have to pull the details from my primary desktop system where I keep those notes. It may be a few hours, but I'll get that to you as soon as I can.

Okay, I couldn't leaving you waiting. Here is the info...

Here is a description of the problem and how to resolve it:

By default, the lock screen times out and goes to a blank screen after one minute and no way is provided in the Windows GUI to change this. After implementing the registry change below, the user will have access to a new setting in the Control Panel to change this timeout. This is especially helpful if you want to be able to see a screensaver run while on the lock screen. The registry entry will expose the new option in Control Panel in the location noted below.

Start by opening an elevated command prompt and then run the command below. It might be easiest to simply copy and paste this:

REG ADD "HKLM\SYSTEM\CurrentControlSet\Control\Power\PowerSettings\7516b95f-f776-4464-8c53-06167f40cc99\8EC4B3A5-6868-48c2-BE75-4F3044BE88A7" /v "attributes" /t REG_DWORD /d 0x00000002 /f

After making that registry change, a new option will be available to you in Control Panel. Open the Control Panel and do the following:

NOTE: Select "View by: Large icons" or "View by: Small icons" when you first open Control Panel. Select Power Options > Change plan settings > Change advanced power settings > Display > Console lock display off timeout

Change this timeout to something longer than the timeout for your screensaver. If I recall, I believe you can set this to zero to prevent the lock screen from ever going blank.

Please do let me know if this solves the issue for you!

You could try the Dynamic Theme app
Dynamic Theme - Official app in the Microsoft Store