We have not tested Galaxy S21. However without doubt in some market areas the call recording feature of S21 is enabled so Boldbeast Recorder works great, but in some areas it is disabled so only your own voice can be recorded, just as previous Samsung flagship phones like S10, Note10, S9 and Note9 did.
Please see  in this page http://www.boldbeast.com/android/call_r … oting.html to use suggested settings to record calls. If it works well, that's OK. Otherwise you should
- Switch on the loudspeaker during a call, so Boldbeast can record the call on both sides normally. Or
- Root the phone, so Boldbeast can fix it completely to record calls on both sides perfectly without switching on the loudspeaker.
If you have rooted your phone, please
- tap "Call Settings - Fix Recording Issues - Enable Rooted Options" to grant root access to the app.
- set Record Mode to "Alsa2 Mode".
Then you'll get perfect call recordings at once.