Yes. It has been reported and the developers are aware of it. There has been some suggestion that an extension might be the cause however I haven’t figured out which one and since it seems to be new behavior with SU2019.3 it would seem like it isn’t really the extension whichever one it might be.
I hadn’t heard about grayed out menu items in SketchUp 2019. But, in activating 2019 you don’t have to uninstall 2018 on that same machine. If there was something interesting in 2019.3 that you wanted to try, but you’re worried about something not working quite right, just keep 2018 around.
Except once 19 is on your computer any 18 file you double click to open will open in 19 and be converted. It’s hard to “try out” new version while still keeping workflow in the old version because the new version tries to take over. Any way around that?