Thanks for updating this @psweb, seems like I’ve been posting on something close to the same thing only a few hours apart from you: having a spinner within only one row of a repeat/table.
As my use-case uses POST API, thanks to your post I was able to come up with an equivalent solution: use a hidden form external to the repeat-region/table with unset hidden inputs. On-click, the hidden input gets set from the row’s unique-like ID, submits the form, and on-success unsets the form’s own input again. The conditional on the row’s styling is whether or not that row’s unique key is equal to the form’s (volatile) hidden input.
Note however, no matter what I tried, I couldn’t get the button inline border spinner to work and used alternate styling on the button.