When you open the Message Filters dialog, filters are shown only for the account selected at the top of the window, i.e. filters are defined per account.

If you only have one account and the window is empty, see if it's still the case in troubleshoot mode (under Help).

Thanks for your answer. I have two different accounts, each with its own filters.

What is the result of troubleshoot mode? It can test for display issues.

Same. One account has it's filters, the other account doesn't.