Maybe im am doing something wrong and if yes sorry, but i put waterfillable on everything in the config but i can not waterfill tiles with cliffs, items, etc.

I just tested again to confirm and you must have something else like another mod that changes things because it for sure works on my end:

Ok i disabled every mod i had except your waterfill mod and tried again. Apperantly some other mod breaks the setting. Sorry for the inconvenience. I should have tried that in the first place

Do you know which breaks it? I'd like to see if I can account for it or perhaps warn people about the incompatibility.

I did some testing and at least one mod was the alien biomes mod from space exploration

I have same issue - certain areas can't be waterfilled... well.. in editor it sais "Noxys Waterfill" on the area, but is land and can't place waterpump on it.
Currently not using alien biomes, but a ton of other stuff - might have to look into it as anoying - strange is I don't think I have anything new, so must be an update in either Factorio or some mod that does this for this mod has worked flawlessly for many great year (thanks for mod!)...

PS!
Used this mod with Alien Biomes previously and not had any issues... but been a while.. 1.0 I think...

PPS!
Me again... OK - think I know what the issue is... seems that when I clear forest with grenades it leaves behind an "entity" called "Small Scorchmark". This seems to block waterfilling in that spot and area around it!!! When I removed them in the editor waterfilling worked like a charm in editor and in-game...
Think this is part of Factorio update - base/graphics/entity/scorchmark/small-scorchmark.png