I'm sure I'm on f2fs. Even TWRP says I'm on f2fs. 3T comes stock with f2fs. This is the output of mount | grep data, but since I'm using magisk I think the output has many partitions and I can't make sense of it.
I think the ext4 tweaks toggle is working fine since it reverts to off automatically when the app is restarted. Thanks!
Here is the output: https://hastebin.com/iwokiramek.hs
But I see also you are using magisk, which creates a hell lot of additional mounts. I am pretty sure my app is getting confused by that.
Now I have to try and search for this in an offline way, as I will for sure never install magisk myself.
Let's see how I can harden that.
No 4.0.0 rom out officially, no sources...