HDMI capture with passthrough is $20.
OP did mot solicit or show that there would be any value in people listing ways that one could circumvent this with preparation.
We all know. You aren’t adding anything to the discussion. Nerds love ignoring the cost of human effort if it gives them an opportunity to show that they know something.
There are lots of arguments I find convincing for this being effective. But not OP's. OP is saying they already do these recordings regularly, but "preplanning" would stop them? No way. They already did all the necessary preplanning by the time they finished typing their comment.
Preplanning could be meaningful for other people, but not for them and people like them.
I only mentioned price to make it clear that the level of effort to make the purchase falls within the level of effort they have already established.
I have a systemd timer that clean files older than 24h at startup because the point is not to archive content without consent.
If I ever can't do that I would just use an usb3 screen capture card and record from a second device.
I'm an example of that threat. I'm a freelancer who often has video calls with new clients. Sometimes I surreptitiously screen cap demos or presentations. It would be very difficult to use a phone that way without breaking the conversational flow.
Other supposed workarounds would require much more preplanning. Like I'd need to know that there was something worth capturing.