I bought a Samsung Note 20 Ultra 5G snapdragon n9860 version hong kong but 5G does not working in France on 3.5 band and I don't know why I tried to reset network settings and also created a new one access point but all that does not work and my operator supports 5g I did a search on the internet and found that there was a problem on Android 10 that the 5g does not work and that was on Android 10 but now with Android 11 has the same problem
You need to take car that bands are supported, it's nothing to do with the OS but with the modem. You will not get 5G in France on a device from HK. See Samsung Galaxy Note20 Ultra 5G Dual-SIM SM-N9860 (Unlocked, SD865+, 512GB, Mystic Black) - EXPANSYS ...
There's a hidden command to "whitelist" 5g bands that are blocked on HK models. Google for it.
I did that and 5g works perfectly in the UK on Vodafone and EE