NextCloud is generally slow, but with photos - it's unbearable slow. It has multiply layers of cache, which make everything slower(?!), it's slow to show thumbnails, it's slow to go from one photo to another. Basically it's unusable for sharing photos.
If you want to self-host your photos, and you don't mind non-free software, you're welcome to try out https://photostructure.com (disclaimer: I'm the author). The beta is available for free in exchange for your feedback.
PhotoStructure is especially applicable if you want a cross-platform solution (mac, windows, linux, docker), and don't want to be tied to a specific NAS or cloud vendor[1].
Every time you open the home page you see something new, as PhotoStructure picks out random "samples" by year, or by camera, or by keyword. It's fun to see photos you haven't seen in a while!
My experience with photos in Nextcloud was vastly improved when I setup the Preview Generator app [1]. Still not blazing fast, but makes the Files app usable again when browsing folders with lots of photos. Significantly better than before.
