The minimum required LGI version for Awesome 4.0 is indeed 0.8. Awesome 4.1 will check this at compilation. This was due to a lack of tests of the menubar module (the least unit tested part of Awesome).
Ref https://github.com/awesomeWM/awesome/pull/1350 https://github.com/awesomeWM/awesome/pull/1072
