Lightroom unusable slow on HIGH end pc

By far the biggest issue with Lightroom performance on windows is Antivirus software and hard drive indexing. Make sure the Lightroom catalog is whitelisted (i.e. do not scan) with any antivirus/malware removal software you are using. Also make sure that your catalog and the camera raw cache is on your fastest hard drive - preferably a SSD drive and that that hard drive has at least 25% (preferably more) free space. The actual images can be on any drive but the catalog access being fast is essential.

Here are some pointers for your list.

1. Good. Make sure Classic is at 10.1.1

2. Always a good idea

3. This doesn't help with speed. In fact, the only thing that speeds things up is to at import use "embedded previews". Do Not check 1:1 and do not choose to render smart previews. The latter are useless except when your original images are offline when you for example take your laptop but not the external drive your originals are on.

4. Yes but previews don't help with loading images in develop. You should set the preview size to the setting that says "auto". This prevents the computer from having to recreate previews every time you load an image in the library browser in full screen but again has no influence on develop.

5. That's wise. it only has the potential to slow things down. If you get to a steady state where all xmp has been written you might be able to turn it back on. You really only need this if you don't back up your catalog or when you access your raw images through bridge and photoshop directly (i.e. you browse in finder/explorer to your images and open them from there directly instead of from Lightroom.

6. Not necessary in general. The cache needs to be about as large as your typical editing session number of images times the typical size of an image. So if you typically shoot and edit about 200 images each of 25MB size for the raw, you only need 2.5 GB cache. If you shoot 1000 images (again use embedded previews to speed that up!). Then quickly cull down to 20 keepers and edit those, you need no more than 500 MB cache. No need to make your cache that gigantic and generally does not deliver a speed up.

7. Rarely has an impact but it can't hurt

8. Keep that on in general except if you have an unsupported graphics card. It's way faster with it on especially if you have a high resolution screen.

9. Generally windows should automatically ramp up if more performance is needed but this can't hurt if you are on a power supply.

10. Really won't do much except if the image you are working on is synced and your internet is slow. You have to explicitly mark an image for syncing.

11. Definitely do that. It is another major cause of slow downs.

If none of this helps, check your system monitor and see if there are processes that are hogging memory, CPU or graphics card memory. There is a bug in the current Lightroom Classic that only manifests on windows machines with  certain GPUs where it will slowly fill up the GPU memory and when it is full you get crazy slowdowns. This is fixed by restarting the machine. It seems to be random who experiences this bug.

Hope some of this helps.

What version NUMBER of Lightroom Classic are you using? We need the version NUMBER and not words like "latest" or "up-to-date".

What size are your original images in pixels? (do not tell me megabytes)

What specific actions in Lightroom Classic are slow?

Are you doing a lot of brushing and/or a lot of spot healing?