I would probably mention these first and foremost, excluding ones already mentioned:

• Sakura Quest — basically about this woman accidentally getting roped into a small town’s tourism micronation gimmick. This one’s the GOAT honestly. Super strong recommendation from me.
• Barakamon — about a calligrapher who gets exiled to a small island. Really relaxing vibes. One of my favorites.
• Cells At Work — it’s like Once Upon a Time… Life, except way better. It’s also like Osmosis Jones except better, because apparently personifying the cells of the human body is not actually a particularly unique idea. Anyways, point is that 9/10 doctors recommend Cells At Work. It’s great.
• Lupin III — super long-running series about the grandson of the famous master thief Arsène Lupin. Part II is the most classic and has a great dub. It’s episodic and fairly formulaic so you can jump in at any point.
• Aggretsuko — Netflix x Sanrio furry office comedy-drama basically, where the main character basically has this death metal persona. It’s a lot of fun.
• Library War — takes place in an alternate timeline where local governments in Japan have established basically militias tasked with protecting libraries from raids conducted by the central government trying to ban books.

I could go on, but I think that’s a good amount of very safe choices, though I don’t know how many of these would be considered to be “popular” as such. You can of course also use something like Anilist to find anime with the tag “primarily adult cast” and sort by popularity, but I dunno how reliable that is, like if it includes or excludes things it shouldn’t.