ghenoeghen

I think you are wrong here https://en.wiktionary.org/w/index.php?title=Reconstruction:Proto-Germanic/ganugan%C4%85&diff=prev&oldid=53853693 It is a quirk of Dutch orthography that [u] is written as "oe"..

Cf. en: good nl: goed de: gut

Please don't tell me they are from different origin just because of the spelling.

Rua knows that <oe> is /u/. It's that (Middle) Dutch /u/ comes from PGem *ō, not PGem *u.

Indeed, the descendant of this verb in Middle Dutch, if one had existed, would be *genōgen, whereas genoegen is a derivative of *ganōgaz. Note the difference in the vowels: ō > oe, u > ō.