There’s something about writing settings where magic and tech co-exist that I just love. So many possibilities for them compliment each other, to work together where one fuels the other or otherwise joins hands into becoming magic-tech, or just the fact that low-tech and high-magic are somehow seen as the norm.
I’ve had readers be confused about the time period when they noticed there was both kitchen magic and tech like TVs as well as lanterns, and on the one side I get it. I get that you have a certain expectation when it comes to fantasy worldbuilding. But on the other hand, it’s fantasy! Realworld time periods and rules don’t necessarily have to align in these worlds, as long as the inworld logic is consistent.
And what’s not to love about that? There’s multiple ways to add in tech and magic while allowing variation. Maybe certain tech is only accessible to some people. Maybe certain gadgets and spells are restricted to rituals or cultural events. Maybe your character simply prefers one thing over the other.
That said, there’s a lot to say about needing proper exposition methods to properly convey how your world works so your reader doesn’t get confused (too much). You have to setup the world’s baseline, what’s deemed normal, and do it in such a way that it is engaging to read. The way your worldbuild really depends on what your style is as a writer, what your story needs, and the medium and length of what you’re working on.
In any case, there are so many different things you can do with how advanced, how accessible, and common views can play intricate roles in how you create the tech and/or magic in your world, and that includes historical/low-tech settings. By all means, combine your steampunk or dieselpunk settings with fantasy. Have your medieval fantasy settings. Do think though about how there are lots of ways you can still play and explore in multiple and meaningful ways in what tech and/or magic mean to your story, your characters, and your setting.