Eh, you'd want something like this to run something custom, because there's going to be a lot of iteration and it'll be harder to push things through a distribution they don't control.

It seems to be Debian based and has some customizations to make work w/ Android apps nicer (Halium support).

I would personally prefer PostmarketOS, but I'd be fine w/ that being a community effort as long as Furilabs doesn't block installing alternatives.

It is based on Debian (Droidian to be specific I believe), which to me reads as a fork or maybe a distro flavor with out of the box tweaks to specifically work with the hardware they are selling.

They say they aren't stopping you from installing anything else you want on the phone, they just aren't going to offer help getting a different OS to work, which is reasonable to me.