From How can I manually delete old backups to free space for Time Machine? it is possible to delete an entire Mac's backups, or specific folders by date from Terminal.
sudo tmutil delete /Volumes/drive_name/Backups.backupdb/mac_name
sudo tmutil delete /Volumes/drive_name/Backups.backupdb/mac_name/YYYY-MM-DD-hhmmss
To delete one specific file or folder throughout the entire history, received wisdom is to right click inside "Enter Time Machine" & 'Delete all backups of…'
This, however, appears to do nothing at all.
In this particular instance, Time Machine, in its infinite wisdom has at some point in the past year decided Downloads is now Downloads 1.
Switching off Automatic Updates & adding the Downloads drive to the exception list removed one copy, but only in newer backups. It has left the rest of the history intact, from the beginning, right through when it first decided there were two Downloads drives, a year ago. These versions therefore appear to be orphans. They don't belong to any current drive.
This has now left the entire history with a name change half-way through.
Setting it to 'delete all' from both the first date [Jun 2021] & latest date now changes nothing at all. [I understand this is only triggered when you Cancel back out of Time Machine & may take some time. I gave it 4 hours, nothing appears to have changed.]
So, I'm left with trying to see if I can persuade
tmutil to deal with it. Not the entire Mac, & not one date at a time - there are 100 individual backup instances in the history.
Usually when Time Machine fails [which it does with alarming propensity], the only recourse is to erase the entire drive & start over. It would be nice, for once, to not have to do this.