I have a few PIs, one of which is exclusively a NextCloud server using the pre-made NextCloudPI image.
Just updating, and it's recommending apparmor.
Now, I've been around Linux a long time (I use Arch exclusively on my desktop and laptop machines, and have used various distros (previously Debian) exclusively for more than 10 years, and have never even encountered apparmor.
I see it's a kernel module for hardening security, and reading up on the wiki, uses profiles for restricting applications access to various sub-systems.
Q. Do I need it and is it likely to cause me any problems?
NB. The cloud server is accessible externally.