I used to be a big fan of the Samsung Gear VR. I used it with my Galaxy S10+ and even for watching things like movies as well as playing some VR games. However, it has been common knowledge for around 2 years that the S10 was the last phone to support the Gear VR. I believe Samsung and Oculus decided to part company, and therefore any further phones after S10 were unsupported.
Of course the S21 Ultra would never fit in the VR headset form factor, and if having researched it properly then it should have been realised. The S20, S21 ranges also do not have any support for the Oculus store or software, so even if you were able to connect it physically into the headset, then it will not work as the software cannot install.
Here is an old article from 2019.
I am also disappointed with the fall out between Samsung and Oculus and found this to be a nice toy. However all good things come to an end... and I have invested in an Oculus Rift S for my PC to get my VR fix.
p.s. the S21 ultra is awesome, but I do miss my quiet night movie showing through my VR with a virtual cinema room and Bluetooth headphones...
There is a new adapter you can buy to use on your 21. I bought it and it works fine I Just can't figure out how to access any VR things on my GEAR. I with Oculus would have stayed put, because now in order to use them, you have to buy their head gear and it's easily $300 to $400.
Yeah for the first time I years I think I my have to part ways with samsung. They never tell you anything from the BS with the chargers, plus no headphone jack now this! I need a new phone compatible with VR. Samsung going backwards. Disappointed. Apple seem the better option lately