On normal (non-flow) pages, undoing a revision still allows anyone to see the removed content directly from the diff or the watchlist (in both cases there a link which allows this).
However, currently it is very difficult to figure out what to do to see which content was hidden by someone. The message
This comment was hidden by Who
should have some link (e.g. to Topic:...&action=history) to make this easier.
See also:
T73558: Hidden topics disappear completely with no trace
T59058: Flow: hide actions should be present in the logging table.