Many smart devices that have youtube functionality(tvs, refrigerators, consoles, cable boxes, etc), have limited or no ability to support that functionality in hardware, or even if they do, it might not be exposed.

Once those devices get phased out, it is very likely they will move to Encrypted Media Extensions or something similar, I believe I saw an issue ticket on yt-dlp's repo indicating they are already experimenting with such, as certain formats are DRM protected. Lookup all the stuff going on with SABR which if I remember right is either related to DRM or what they may use to support DRM.