Is this something that happens down the road? I've had nextcloud for probably 6 months now and while technically I've had a couple problems, they were self induced. I haven't heard of/seen maintenance mode.
Of course, just before I was ready to wipe it all and start with the AIO container my partner started intensively using the calendar (switching from paper, finally!) So I need to spend some time with it and migrate properly without her having any downsides. When I do I will also set up EuroOffice and experiment with that. I'm rather looking forward to that. In that sense it's a real "lab" :)