Replying to
@idzie@kolektiva.social
@idzie I'm not an expert either as I only had a two week university class about Central European species. But from everything I know about lichen identification, Rusavskia elegans seems to be a pretty good guess.
Funfact: in this class I presented a paper about the viability of R. elegans after being on the ISS for 18 months (it survived)