@douxy1 The downloads on that page take too long to download because of the limited download speed set by the server.
Instead, I went to http://www.2l.no/hires/index.html. In the latest Opera, Opera Beta, and Opera Developer on Linux Mint 20.2 (Cinnamon), I played the 24/96 and 24/192 stereo flac files (by Hoff Ensemble) on the top of the table no problem. Do those ones play for you?
Have you followed https://www.reddit.com/r/operabrowser/wiki/opera/linux_libffmpeg_config to add proprietary codec support to your Opera?