For Tapas, you can still show nudity and sexual content to an extent.
Upper nudity (both male and female) can exist outside of the mature tag. So you can show breasts and not need to put them behind a tag or even censor them.
When it gets into sexual content or full-on nudity, yeah -- you gotta add the mature tag on Tapas. And trying to show actual penetrative/oral sex needs to be censored in some way. You can't make it straight up pornographic.
As far as I know, Webtoons is much stricter (though again -- that can depend if you're featured or canvas)