seems like #2370 was too short-sighted as

• the cyclic imports apparently are back in 3.4.3, see Circular import error (again) in 3.4.3 pyca/cryptography#5794
• Building PTB via setup.py apparently fails as for some reason this tried to build cryptography from sources? At least on RTD
• There is currently a heavy discussion in progress in Dependency on rust removes support for a number of platforms pyca/cryptography#5771 as apparently the usage of Rust code in v3.4 has broken CIs of a lot of people

We'll need to check out

• How this affects our building process
• How we can reasonably protect our users from install problems. Mind you, installation problems of 3rd party deps is not fully our problem, but if the majority of our users can't install it, then our package is worthless.

One could just pin cryptography to < 3.4 for starters and just wait a bit until the dust settles …