You probably don't get the purpose of the community. At feddit.de, you have no shortage of communities from !femjungenmaimais@feddit.de to !falschparker@feddit.de, but similarly to Czech subreddits, we only have two, separated by language:

• !cesky@czech-lemmy.eu in Czech
• !czechrepublic@czech-lemmy.eu in English

So !czechrepublic@czech-lemmy.eu is not exclusively about the state. It is supposed to be an alternative to r/czech, discussing anything “Czechs” might be interested in, as opposed to broader audiences like !europe@feddit.de. This is purposefully vague and highly inclusive.

I would suggest you to consider joining/posting if you meet at least one of the conditions:

• Czech speaker, any level
• culturally Czech
• has been / plans to go to the Czech Republic
• interested in anything about our country, culture or life
• have content/question that people who meet the above criteria might want to respond to/answer, as opposed to people in or other broader communities
• if you read this far, you 100% qualify

If you're still unsure, look at some posts at r/czech, not necessarily top ones, and see what fits. There is a large gray area, for example this map is unlikely to classify as Czech-related but this one could despite both having been created by a Czech.

As for topic separation, r/czech has tags HUMOR/META/PICTURE/POLITICS/CZECH MADE/QUESTION etc. but not only does Lemmy not support them yet, the current amount of content is more than manageable without them. After growing enough, r/czech was “split” into other subreddits, like r/czechmemes (CZ/EN memes) and r/okkamaraderetarde (CZ Gen Z dank memes).