There’s actually a whole thread where people put their IF ideas/inspiration they probably won’t use! It’s a little disorganized, and some give too little/too much information, but I’m sure you can find something that sparks interest!
I’ve found that, when in a slump of ideas, trying to magically make things appear on their own by mashing stuff together doesn’t work, as the product feels stilted, choppy. It’s better to surf through things you’ve enjoyed and try to take a certain plot thread in a different direction; rename the characters from a beloved book, make it from the POV of the usurped king’s wife instead of the plucky hero, rework any worldbuilding that’s a bit too unique to the book, and bam! You’ve got yourself a new story! Or, as I linked above, browse through others’ ideas until something gets the idea juices going!
Once you have a sense of what you might want to write, you’re probably going to want to just dive in; considering this is a short practice IF, you can reword and rework things later; but with an idea, I find writing a rough draft of how a scene might play out (usually the one that pops into your mind when you get inspiration,) to help with figuring out the tone, the narration style, and just how you want to go forward.