I don’t want to spill the beans on what I’m currently using since I don’t want it to be patched. But I can tell you what I use to use before my current config. Since apps and devices have updated to a point I found better ones.
I use to run an old Samsung Tablet with USB C video out and one of those Amazon bargain bin tablets with HDMI.
Once this bad boy strips the HDCP any old HDMI recorder can record the signal. At a time I used the Elgato HD60, but I’ve moved on since due to HDR content causing it problems.