Just registered to respond to this, I was having the same issue with the Seeed Xiao nrf52 on the latest Arduino IDE.
Turns out that this post on the Adafruit forums fixed it for me:
viewtopic.php?p=879584&sid=37d8b4cd1db014be59936a795c392597#p879584
Create a sym-link to your adafruit-nrfutil from ~/.local/bin and the IDE picks it up during it’s regular $PATH trawling.