Comments and likes of captures/clips under "Social" tab are not tied anymore to the same...

Have you checked under Watch through your profile? There is a Manage Capture tab. Go there. Look for the far left tab where it says On Xbox Live. Try changing that tab to On this Xbox. All the clips should be saved there if not for the first option. It's
kind of like a backup saves for clips.

To capture gameplay either before or after the fact, follow this guide:

https://beta.support.xbox.com/help/friends-social-activity/share-socialize/capture-game-clips-and-screenshots

Captures can be found under the captures tab, the app can be found under the community tab last time I checked

Can you see you clip in the home tab 'recent captures?

Hello PCGC,

Sorry to hear you are having trouble with your game clips. Remember that you can only trim clips that were created on the same Xbox console. If you've uploaded a clip from a different console, you have to trim it from the same one.

For the sound issues, it may be due to your chosen audio settings. Under Settings, then General, and then Volume & Audio Output, check what your Headset Format is. If it's Dolby Atmos or Windows Sonic, try going back to Stereo Uncompressed. (Another paid alternative is DTS Headphone).

Additional Resources:

Manage your game clips | Xbox Support

Capture game clips and screenshots | Xbox Support

Regards,

Hayabusa