1. Settings->Share->Enable screen sharing (set the password for remote connection)
2. Install xrdp and dconf-editor
sudo apt-get install xrdp
sudo apt-get install dconf-editor
3. Configure dconf-editor
Open the dconf program, expand org->gnome->desktop->remote-access in turn, and then cancel the check of "requlre-encryption".
4. Use VNC Viwwer to connect to ubuntu
Download VNC Viewer | VNC® Connect
Reference materials: ubuntu20 configuration remote desktop - wholeheartedly_operation and maintenance- Blog Park