Slovakia has no entry restriction for anyone but requires a self-isolation upon arrival if you're not vaccinated. This means you will have to stay in your hotel room for 10 days (NOT two weeks) - or until you receive a result of negative test which you can take on day 5. I would therefore skip Slovakia, it's not that interesting anyway and has fairly brutal covid restrictions (I'm from Slovakia and I basically ran away and stayed away for the last year because of the covid nonsense). You would also be unable to do basic stuff without getting tested every couple of days. Also note that hotels may become closed to the general public, or require vaccination if situation deteriorates.
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Within central Europe, Hungary has the most lax approach, I would look into it. If you arrive by land, there are absolutely no entry restrictions. Neither are there any domestic restrictions once you're there - it's 100% business as usual. If you fly into Hungary, you need a negative covid test but that's it - no further restrictions.

Scandinavia is also fairly open and it is possible to visit it under certain circumstances even if you're not vaccinated.

The key is getting into the EU. Once you're in, many countries will accept you even if they ban direct arrivals from the US. Poland is one example, if you're interested in central Europe region.

False. There are many European states that accept people with a test.