I say this a lot, but "nomacs" image viewer/editor. I take a lot of time lapse videos and I have directories of like, 50000 identically-sized images each on a smb server over gigabit ethernet and nomacs can open from a directory and quickly cycle through the photos using the arrow keys, without resetting the current pan/zoom setting (important for me), without any trouble. It takes about as long to open the directory of photos as it takes for my samba client to download the directory data.

It also has a lot of cool little quality of life features, including lots of shortcut keys for overlaying metadata and such. It has basic image editing capability as well. The only other image viewer I use is digikam, which is more for organizing personal photos. Otherwise it's all nomacs, baby.