This page lists and compares a bunch of different options. Just quickly eyeballing it, Nextcloud Photos/Memories (not sure if they're separate apps from the main Nextcloud you mention), LibrePhotos, Immich, and PiwiGo seem the best options.
Free and Open Source Software
If it's free and open source and it's also software, it can be discussed here. Subcommunity of Technology.
This community's icon was made by Aaron Schneider, under the CC-BY-NC-SA 4.0 license.
Immich all the way. It is very similar to Google photos in terms of UI and features and is being actively developed. You can create shared albums with unlimited contributors and also share an album by its link.
I have used Nextcloud before, but the feature set (even of the memories addon, which is supposed to be better than the default photos app) is severely lacking and Nextcloud is incredibly slow compared to immich.
@maki I remember there was a photos plug-in or something for Nextcloud that allows you to see the photos in a gallery (Kinda like in Google Photos).
In the Lemmyverse for self-hosting Immich looks very popular (despite their warning : The project is under very active development. Expect bugs and changes. Do not use it as the only way to store your photos and videos!)
The old skool Piwigo might do for you ? https://piwigo.org/
Not OP, but I’ve been low-key looking for a good photo album software too. This looks interesting. Thanks!