Just adding my own experience, Nextcloud AIO runs plenty fast for just me (family is slow adopters) but its simple user interface is slowly working for them.
I run it in an LXC with access to two cores of an i7-9700 and 4gb of ram.
All the files are stored on an old usb2 external hdd.
Obviously that set up won’t scale well and the hdd will be the first bottleneck but I notice no performance issues and as a shameful windows user the way it ties in like OneDrive is great.
I can also just mount it as a network share for my Linux computer.
I do use the calendars and other features though.
Unless they are in a monogamous relationship, it shouldn’t be a scandal. They make it hard for themself by crying purity all the time.