Are you alright otherwise? Because sure it can just be your own normal at this age, or getting burnt out on a type of content. But (and sorry if I'm overstepping, but I know I needed people doing just that many times in similar situations) it could also be a symptom of depression or getting near / being in a "down" episode of various mental or neurological things, or a side effect of certain medications.

If you are okay in other aspects of life, pick up more stories rooted in reality or speculating about our future (could become real). Or turn it into a game to research and figure out how the fantasy books are real, all the good ones are full of allegories and meaning, and it's fun to dig them up (warning: don't do HP unless you're ready to deal with some bad stuff)

But if you're not okay... Struggling with other hobbies. Not caring what you eat because it's just fuel when you used to cook or had little treats. Cancelling plans because they aren't worth the effort. Change in cleaning or personal hygiene routines because some parts of it are pointless or you don't have the energy. Doubting friendships, not finding meaning in them or getting paranoid or feeling like everyone hates you. Memory issues, too much or too little sleep, losing time... Reach out for help, do some therapy if you can, get your meds adjusted or changed, etc.