Generally speaking, there is not much popularity for the games that I am interested in in my area. I am not a big sports fan, however I am a great fan of NASCAR, MMA, and volleyball. If you have any good ideas, let me know.
NASCAR is enough familiar with crypto. I have several times read the news about NASCAR which has sponsorship by crypto like bitcoin and dogecoin. But as you said, I don't find many betting sites that listed NASCAR, maybe have several sites, but didn't accept crypto as payment. About volleyball where you have mentioned too, I ever seen volleyball women listed on betcoin.ag and stake. Maybe if you have a time, you have to look it again.
I've done some research on my own and I am only able to find well rated betting platforms that are into NASCAR betting, but they don't have crypto deposit opened, but I do find one called BetUS.com, this is the best I could find, they have some amazing first deposit offers right now, up to 2500$ and they accept crypto deposits with bonuses as well, all other sports that are hard to find on today's online casinos are available on this website and they also have mobile app.

well, this BetUS.com site that OP posted, is a shady site, I consider it to be a shady site because this site has many complaints, the many complaints can be seen here:
https://www.trustpilot.com/review/www.betus.com.pa
There are a lot of complaints about this site so I advise people not to use this one because it has a lot of accusations, and looking at the dates of the accusations it seems to me that they are somewhat legitimate accusations, I hope people stay away from this casino. if people want to bet on NASCAR then they better use stake.com because it's the best casino and the most reliable casino, don't fall for this bonus greed, that's just to attract people and deceive them. and I suggest that people take the time to read the reviews that are on this link site
stake, Bet365, William Hill, or Bovada, they all offer betting options for NASCAR, MMA, and volleyball.
Im gonna try out, thank you! I rarely bet with large sums, so for me minimum bet limit is sometimes a problem, and also issues with withdrawal are a bit annoying... Which one is the best among these in your opinion?
maybe i'm wrong, but as far as i know Bet365 didn't accept cryptocurrencies, they accept deposits by bank card and ask for KYC, at least it was like that in the past when i checked this casino because i wanted a casino to watch games in the past, if you are looking for casinos that accept cryptocurrencies, then you have to use stake.com because they also have NASCAR