

uMatrix is no longer maintained and is largely redundant. Mullvad Browser doesn’t force DoH either, it’s just enabled by default and you can turn it off pretty easily. In fact Mullvad’s addon warns you if you’re using DoH with Mullvad VPN, at least as far as I can remember (I don’t use a VPN currently.).
The automatic connections are not arbitrary either. Your browser, addons, or uBlock filter lists not updating in a timely manner is much worse than the miniscule amount of data you’re sending to the outside world.
You could try using Cromite just for this.