I feel maybe that's a dovecot issue? Or a spamassassin issue?
In my setup it seems "normal" that spam sent to aliases gets in the "catch all" instead of the mailbox of the user that has that alias. Very infuriating as I had to tune down the spam filter to block only the most obvious spam as false positives get "lost"
Although since 3-4 months ago I didn't receive any misdirected spam in the catch-all mailbox, so it might be that's now it has been fixed (I'm one of those guys that run updates automatically unattended because my hobby is fixing problems when there's a breaking feature after update)
Software solutions: streamfab or anystream (RIP)
Hardware solution: a $5 HDMI splitter from AliExpress to remove hdcp (it must be no name chinese AliExpress stuff, branded splitters won't remove hdcp) + HDMI capture card