I found instances of રુ ligature in Saarth Jodanikosh which is a thesaurus and spelling reference book from 1949. I’ve gone back and checked a few examples for both cases. Almost all default Gujarati fonts have the ligature, so you’ll see a difference between રુ and રુ.) (I’m using ZWJ to break the ligatures here. This is consistent with Gujarati rū (રૂ) which was probably derived from રૂ.
However, as far as I remember, Gujarati ru is written normally with the u-matra below the letter, રુ. In both Sans and Serif Gujarati, the letter combination રુ (ru = ર + ુ) is rendered as a ligature where the u-matra is connected to the right side of the letter. र = Devanagari Ra (u+0930) (only for comparison).રૂ = ર + ૂ (u+0ac2) (Gujarati vowel sign Uu).રુ = ર + ુ (u+0ac1) (Gujarati vowel sign U).So I created this issue on Google Fonts back in September, but it is relevant here as well.
