Yea some people are stuck. The Thai government has extended visas for foreigners stuck here but that maybe running out soon.

I've heard a few people are stuck in Thailand since March

Are any foreigners stuck in Thailand and can't leave? what's the visa situation like?

Some places are still limited but things like bars and clubs are opening up with some restrictions. Schools are partially opening up as well.

Not really, the city is open to locals and anyone from other Thai provinces. However, Thailand is shut to foreigners at the moment.

Is BKK totally shut down right now because of Covid-19?