@hypolite I found a trick to see notifications and mark them as read! This is a somewhat stupid, cumbersome, and impractical way; yet it worked.

In practice you have to open two browser tabs, logged in with an account other than the forum one (for example, the account that controls the forum account).

At this point on one of the two browser tabs, you change your account and switch to the forum account.

As soon as you've browsed two or three pages, a funny thing will happen on the other browser tab:
1) the interface remains that of the normal account and will not yet have transformed into the typical interface of "forum" accounts
2) however the logged in user is the new one, and therefore will be the "forum" user

In doing so, you will see the bell icon (as with the normal account), but with notifications from the "forum" account