Krita 4 beta 1 runs fine,

4.0 and 4.0.1 open for a split contact and then crashes.

a few weeks ago it was working fine.

I am running El Capitan

I tried unsinstalling reinstalling rebooting etc etc

We did update to a new version of Qt, but that should still support 10.11 and though I always have to google to see which cutesy codename is which version number, that seems to be el capitan. And I do build with the 10.11 SDK, too.

I don't test on 10.11, though, because I only have one mac, and that's always on the latest version of macOS. Do you get any crash log, any hint if you start krita from the Terminal (open terminal.app, enter "cd /Applications; ./krita.app/Contents/MacOS/krita" ?