In Czechia, ISPs are forced to block certain websites, but exact method is not speficied. Today, they just block it on DNS level, as that is simplest and effective enough (although easy to circumvent). If ordinary users were using DoH, then ISPs would be forced to use IP based blocking

This was one of the concerns brought up at the UKNOG panel:

Currently there is DNS blocking (e.g. gambling sites in Poland), and it handles most cases. If (too many?) people start circumventing that, will a government start insisting on more invasive measure (e.g., DPI)?

The government wrote a white paper about this because they proposed yet more blocking (for the whole anti-pornography thing where they want you to go buy a "pass" to look at porn) back in 2018.

The ISPs are not inclined to pay for DPI or whatever other nonsense, even if they believe it could be effective, which it probably can't be. Government does not want to take on a major budgetary extra to pay for something that's already unpopular. So that leaves it not getting done. Much hand-wringing.

The government already acknowledges that Tor completely defeats all existing attempts to censor the Network, but they supposed that DNS blocking is affordable and good enough. So, we make it no longer "good enough" and then too bad for their stupid policy.

AFAIK the piratebay block works at more than the DNS level. As in, navigating to the correct IP still gets you blocked.

Depends on the country. The Internet freedom index talks about what each country limits, not all do in any significant manner.

First, these things are generally country specific. Is there an EU Directive that makes it continent-wide?

Second, given countries in the EU are fairly democratic, this is done via acceptance of the voting public because they elected the representatives. They can always have the law changed if they don't like it.