I'm using the Raspberry Pi 4B with 2GB of RAM. I have no problems with WIFI connection, though. But I can't make connection using
nm-applet it shows "device not ready" under "Wi-Fi Networks". Anyway, I can connect to WIFI using the built-in (LXDE or PIXEL, I believe) WIFI manager.
Summarising, I'd like to have possibility to connect to WIFI on wlan0 (Raspberry Pi 4B built-in WIFI interface) using NetworkManager.