Andrew

The “I’d buy that for a dollar!” guy from Robocop.

You can set a gif’s FPS yeah. There’s an app called gif.ski that lets you play around with this - add a folder full of PNGs to it and render a gif. The lowest the UI lets you select for FPS is 1 - I made one and stuck it here so you can see what that looks like.

You can use the same tool on the command line if you want a half frame per second rate, e.g.:
gifski --output interesting.gif --fps 0.5 --quality 70 *.png

I don’t know if there’s any tools that’ll do that - I imagine it’d be an animation that you’d need to tediously build frame by frame. Gif is especially inefficient to simulate slowness because you need a new frame even when it’s the same as the previous one, so the file would be massive. So you’d want to convert it to MP4 (which anything hosting it would probably do automatically) or use webp - this doesn’t have particularly widespread support but it lets you create animations with a ‘delay’ element so you can hold certain frames. An example of that is here: https://lemmy.world/pictrs/image/218d951c-67b3-4589-ac94-8f661b32a8fc.webp (wait for it …)