Youtube uses cubic projection for its videos, but most other things, like VR headsets, natively use equirectangular. Yes, there are players that will play either, but I am shooting for the native format of my Apple Vision Pro.
A quick way to convert them is with ffmpeg. You can tune the parameters to your liking, but the “v360=eac:equirect” is the filter that works the magic.
ffmpeg -y -i input.mp4 -vf "v360=eac:equirect" -c:a copy -c:v hevc_videotoolbox -q:v 52 -tag:v hvc1 output.mp4