Hi! This is a question almost every artist struggles with at some point in time, so here are some things that might help.
Any knowledge or experiences you have can be used to inspire ideas. I think some of the most interesting ideas come from one’s own observations and specific details you’ve noticed, or things you find interesting. For example, I personally enjoy learning about physics and plants/animals. I like to experiment with what might happen if you were to adjust the variables of physics, or taking interesting aspects of unusual creatures and incorporating them into designs. If you have any hobbies or like to read/watch videos about a specific topic, that’s a great place to start.
Two brainstorming techniques which might be useful are word association and clustering. For word association, you start with a base word (ex. magic) and come up with as many related words or adjectives you can think of (ex. witch, mana, whimsical). For clustering, you create a “network” of words or themes which are related, starting from a base word or theme. Circle each word and connect related ideas with lines. Both methods are useful in different ways for coming up with, or developing, ideas.
There are a lot of idea generators you can use if you have difficulty getting started. One generator intended to be used for art is
ArtPrompts, and another, more generalized generator, is
RandomGen. You can also use writing generators like
Plot Generator. There are tons of them for pretty much any topic imaginable if you search on Google.

One thing you haven’t mentioned which can be pretty fun is joining in on art challenges or game/art/writing jams, like Inktober, Ludum Dare, or National Novel Writing Month. Working on something at the same time as, or in conjunction with, lots of other artists is a great way to get inspired to make things, get feedback, and meet some other artists.