@klntsky there is fediverse.network and fediverse.space that show some stats, but in general there is no easy way of knowing that, aside from what admins disclose.

qoto for example has policies on instance blocking nicely outlined in the about page. It doesn't block other instances, and silences only in case of active harassment. That said other instances are free to block qoto, so strictly speaking no instance can guarantee it federates with every other instance by itself.