It helped me a lot to play around with different styles, instruments, softwares or even arbitrary limitations. It'll be a step backwards at first, but forces you to discover new things.
I agree with getting some drums, but more VSTs hasn't helped me personally - it's mostly just more clutter, more things that do the same things your stock plugins can do if you learn how to use them. SPAN, OTT, TDR Nova, Youlean Loudness Meter and Vital (all free) are the few exceptions to my "rule".
There's a free book I've been reading that I think addresses your question of "how to have fun again" - similar to what the first comment in this thread said.
Try to make something deliberately bad. Like, aim for so-bad-it's-fun? Or comedic parody tracks?
Or maybe make little tracks whose purpose is firmly communication rather than quality. Such as soundboard-type effects to use as gif-equivalents when talking to friends - either to mess with them or to communicate "this is my mood right now" or what have you.
Or maybe take a break and do another kind of art for a bit, then come back.
Practice copying other people's songs. Changes, vibes, subject matter. Mind you, this is only for practice. But it is the way plenty of musicians develop their musical grammar in order to use the language in their own way. See: jazz
I started an all-trans punk band online, and my usual music is singer-songriter. The new project really pushed me, and turns music making into a social activity! I also started another solo project that is 100% cello covers of contemporary songs (last one I did was "girls just wanna have fun"). Both of these projects push me out of my usual, and breathe some fresh air into my music. Maybe you could find some ideas that pushes you out of your comfort zone?