Docker latest points at V21

I’ve moved my Nextcoud instance from a different VPS and now I’ve installed with docker.
I’ve noticed that using

image: nextcloud:latest

it installs version 21, why is that?
So I need to use

image: nextcloud:23

but in this way I can’t keep it updated with Watchdog.

This is a perfect reason to just use numbers and not latest. Save yourself this hassle in the future.

Yes, but why is that?
As I’ve said, in this way Watchtower will not work.

Depends on the maintainer of that image, be it official, linuxserver, ncp, etc.

You’d have to ask them. Either forgot or withheld for some reason.