People live below you?
I am second floor and pulled up carpet that was down in bedrooms. I am concrete with metal joists below. Most concrete requires a ton of work to polish, if it was not poured with that as the original intention. Mine was level, but not flat. My second bedroom is a dedicated workout room. I went with glue down solid California Bamboo, the installers flattened the floor some, and have a mat under my Kickr and bike, and a mat for working out. If you are second floor, you do not need to worry too much about moisture, but protecting against it is never a bad idea.
Two things to think about:
Check your documents to be sure you can replace soft flooring with hard flooring, or what the rules may be. Some condos are very strict. My current place is not, but I read the information, submitted a request, and made the board give me a signed approved copy, even though they said they did not have an issuer with it. I hate being bitten in the butt by stuff like that.
All those videos on YouTube that show how easy it is do your own self leveler compound? It isn't. It is very easy to screw up. Trust me and don't ask how I know.
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"Remember: a bicycle is an elegant and efficient tool designed for seeking out and defeating people who aren't as good as you."
--BikeSnobNYC