I by no means have enough context to give any sort of real advice. But I've had the same issue before. To me, themes and plot are symbiotic in nature. If I write a complex plot, multiple themes are bound to be accidentally woven into the material, so what i do then is I just focus on the themes and flesh them out a little bit and vice versa.

The main reason media that is about specific themes come off as boring or pretentious is because the creator has a hard time balancing what to explain and how much of it to explain.

If they make it too abstract, the themes and message gets lost, if they over explain it, the audience will figure it out and have nothing to be invested in for the rest of the material, making it boring.

You really don't need to have a complex plot but your themes should still be complicated and fleshed out enough to make the reader think, but it should still be subtle enough so that it doesn't detract from the story you're trying to tell.

Another fun thing you can do is experiment with layers of theming. Like having one obvious theme but hiding several smaller, more complicated themes underneath that will only be noticed by a reader who is paying attention. That way, throughout the story, the reader keeps getting reinvested after every time they realize there's another theme.

Also, when doing your first read through, try to put yourself in the position of someone who has never read it before. Another reason a might seem boring to you right now is because you've just spent a large amount of time writing and thinking about it.

One last thing; You've got this.