I discoreved what the issue was. My world IS on 1.14.4 , but it has old chunks from 1.14+.
Aquatic mobs indeed do not spawn in the old chunks, but they do in the new ones that I generated. Still weird considering they should spawn in both.
This bug is not fixed, I don't know why Mojang said it is.
No fishes or squids anywhere in my world.
As the other commenters said above me, this bug is back in the game.
Should I make another ticket for it?
What? It's not a feature request, is painfully obvious that they forgot to add them as valid fuels.
Rip Joergen
Confirmed for 1.14.3.
Mojang it's been 4 years please stop ignoring it.
Confirmed for 1.15.1