ArtSaverApp 4+

ArtSaverApp is a slideshow / photo-frame app for large image collections you have stored in a folder (or several folders) on your disk.
It is mostly geared towards people who want to see their pictures as large as possible, with some information about each image currently being displayed, and with more controls and options.

With ArtSaverApp, you get more control than Apple's built-in screensaver: at runtime, you can, for instance, review previous images (using arrow keys); in the settings, you can control the image duration, image transition, filter out images, and more.
You can also download a companion (helper) app that allows you to turn ArtSaverApp into a surrogate screensaver (see the Manual or the web page).

There is also a companion screensaver that is one of the few slideshow screen savers that allows you to see a different sets of pictures on each monitor in a multi-monitor setup, and with the same set of options as ArtSaverApp. (More details on this in ArtSaverApp's manual, or on the app's web page.)

Note that, by design, ArtSaverApp does not sport fancy visual effects, such as picture postcard, mosaic, or the like! It only offers still images, zoom in/out, and pan & zoom (a.k.a. Ken Burns effect). The goal of ArtSaver is to present the pictures such that you can enjoy them in their full glory.
Note, also, that ArtSaverApp does *not* come with its own pictures; it assumes that you want to see *your* pictures.

Don't forget to go to ArtSaverApp's Settings when you run it for the first time.

Some of the app's features (same for the companion screensaver):
• Can display the file name/path, some embedded "EXIF" tags, and GPS location of the image currently being shown
• Keeps a persistent database of all the images found in the specified folder (including sub-folders). Thus, it can handle huge image databases (250k images are no problem), display images immediately when started, and, does not "exercise" the disk every time it gets invoked
• Handles large image files well (like 100+ MB per image on disk)
• Keyboard controls at runtime (app only): go back to previously shown images, pause the slide show, reveal the current image in Finder, and more
• Display images in random order, or sorted by file name, or sorted by date embedded in the image file. For more details, see the Manual, section "The Order in Which ArtSaverApp Shows Images"
• Many configuration options, such as duration of image, filtering out small images, font size for info, and many more
• Can follow aliases (and symbolic links) during image search

Please note that ArtSaverApp CANNOT access the photos you keep in the Photos app of your Mac.

You can find the complete manual on ArtSaverApp's web page (and in the app, of course).

On the web page, there are further hints and tips, for instance, work-arounds for some obstacles, or older macOS versions.