Exim4 broken after Debian 11 upgrade - Tainted filename / temporarily rejected RCPT

So I recently upgraded Debian 10 to Debian 11, and since then Exim4 is completely broken.

Whenever an email is sent it gets rejected, and in the “paniclog” I can see something like this:

Tainted filename for search '/etc/exim4/domains/mydomain.com/aliases'

In the “mainlog” I can see some more detail:

2022-01-04 23:23:07 Tainted filename for search '/etc/exim4/domains/mydomain.com/aliases'
2022-01-04 23:23:07 H=(webmail.mydomain.com) [] sender verify defer for <[email protected]>: failed to expand "${extract{1}{:}{${lookup{[email protected]$domain}lsearch{/etc/exim4/domains/$domain/aliases}}}}": NULL
2022-01-04 23:23:07 H=(webmail.mydomain.com) [] F=<[email protected]> A=dovecot_login:[email protected] temporarily rejected RCPT <[email protected]>: Could not complete sender verify

I’m not sure where to start debugging this. My Exim version is the following one: Exim version 4.94.2 #2 built 13-Jul-2021 16:04:57

It seems that the Exim4 version is the issue as seen here ( Error sending email - Hestia Control Panel - Hestia Control Panel - Discourse (hestiacp.com)), but there is no solution provided and there is not really a way to downgrade it given that it’s shipped with Debian 11.

Anybody knows how to fix or debug this to get it fixed? Thanks.