Semi solved by switching from one release to another. Oekaki works fine with pen pressure on Manjaro without any oddly specific extra steps.
I am using a Wacom tablet (old Intuos) and a Vivaldi browser. I've installed this wacom driver.
Hey, I've searched the forum and I guess there's no real solution for this, but I want to ask again in case I'm missing something obvious. I'm on Linux (Fedora 31), Vivaldi browser, I use a Wacom Intuos Pro tablet that I've managed to get to work on GIMP/Krita etc. and Oekaki works fine, just without pen pressure at all. It's not a major issue that will stop me from using it but if there's something that can be done about it, I'd like to know. Am I missing something obvious? You tell me.
edit- I don't have Wine installed, haven't tried the JTablet way. Maybe that's what I'm missing lol. But I'd like to know if there's a native library I can use instead
edit2- I have used Oekaki on Vivaldi on Windows without issue.