I'm using a macbook pro 16, use my hotspot frequently in the past on catalina. Upgraded and running big sur beta 9, and was having a heck of a time getting my iphone hotspot to connect reliably. Would connect, but not get ip, or would connect and get ip but no internet. Very frustrating. I found if I connected to my wife's iphone (which I never do), it seemed to work. Or, connecting to a real wifi network, also ok. I did a NVRAM reset, didn't seem to fix. I did a SMC reset, and resolved issues entirely for me. I am typing this connected to my iphone hotspot! :-)