File/Folder deletion from Time Machine

I understand. The implication is that you do not want to back up those large files or folders, which means you should add them to Time Machine's exclusions list: Exclude files from a Time Machine backup on Mac - Apple Support.

Otherwise, it is not possible to specifically isolate and prune them from the existing backup while leaving everything else intact. You can wait until Time Machine requires the space they occupy (which will occur... eventually) or to erase the entire backup disk and start anew. The oldest backups — the ones taking up space for no good reason — get deleted first, automatically. Just let it happen.

If I may assume you intend to use Time Machine to effectively archive backed up items, please be advised it cannot be used for that purpose. TM is not intended to be an archival system. If you delete an item from the source volume, it will be deleted from its backup... eventually.

I'm running Big Sur 11.7 on my M1 Mac Air, and I can still select "Delete All Backups of", as I did in the pre-Big Sur days.

You can't do that, because your Time Machine backup volume is formatted APFS, while mine is still HFS+.

What is is you want to delete?

A Time Machine backup is "read only" and cannot be modified, except to erase the entire backup.