For me, onboard RPI 5 wifi is terrible. It constantly stops and is unreliable.

So I purchased TP link Archer T3U Plus and this worked mostly perfectly until the recent RPI firmware update broke the firmware-realtek driver etc.

So just now I installed this driver:

https://github.com/RinCat/RTL88x2BU-Linux-Driver

And we are working again!

You can disable onboard wifi by:

sudo nano /boot/firmware/config.txt

adding dtoverlay=disable-wifi