Gotta say, I’ve had a similar experience with EE4. I read the EE4 info and it looked like Ubuntu 18 was not supported, so I installed EE4 on Ubuntu 16 - it failed to install PHP. Tried multiple times.
Now I’ve tried it on Ubuntu 18 several times and I get different issues. Bad gateway issues after site creation. THAT seems to be limited to the host. I was using UpCloud. Moved to Vultr and that does not occur. But now I get different issues. Not being able to enable SSL (cannot validate challenge for domain is the error I get) or most recently, it just fails to create the site.
I love love love EE3 but really disappointed with EE4 so far so I may have to use the EE3 fork.