I have just upgraded a J!3 site to J!4. For some reason I couldn't do the upgrade to 9.5.3 on J!3 (kept saying no update found). On J!4 it said 9.5.3 wasn't compatible, but it wouldn't install 9.5.4 - kept giving me errors. I uninstalled it and tried to install 9.5.4 from scratch, but kept getting errors.