Oh, no, it's not 月 either. XD That would be way too simple! It's 冂 plus two inner strokes that don't connect to the sides. (So... identical to 月 but with the inner lines not connected.) Even better, right?

(I do get very mixed up between 月/肉 as side radicals, though. And it's not like the other ones where I never bothered to learn the difference, it's just so hard to actually tell them apart!)

don't take my word for anything to do with characters!

I mean, several places including Baidu and Pleco agree with you that it's a sun radical, so even if that's not the only correct description, it's not like you were wrong! (And the Japanese transcription is pretty clearly 日, even if the others might not be...)