As far as I know the greek keyboard layout is based on the US style alignment, with the characters swapped. The Greek alphabet has fewer characters than Latin after all. The standard quick way to change the input in Windows, and the one I’m using in Ubuntu is hitting Alt+Shift. Spelling Linux phonetically would be Λίνουξ.
Just figured out yesterday that OpenBoard is abandoned and jumped over to Heliboard, thanks to the announcement for 1.0 in this community. The top comment mentioning FUTO Voice Input, was also a great find.
The only annoying part is that I now have to retrain my recommendations for HB, since OB unlike HB, offers no way to extract your settings, and I found no method to access the settings files in newer Android. Thankfully, since HB offers import/export, it will be the last time.