It could be something harder to solve, but the thing that helped me was trying the boring/cliché/obvious advice first. Like p much every "normie" life tip I've followed has made my life slightly better.

Like exercising regularly (made minor aches less common), which lead naturally to drinking less (improved base mood a bit, and gave me my weekends back); reading before bed instead of screen time (paired with other habits made it so I can usually fall asleep within 30 minutes (huge for a former insomniac)); starting a diary (let me converse with myself and recognize long term patterns), then starting gratitude (diminishing returns after a while, but still think it's worth trying); walking/running (hurt at first, but eventually felt great), which lead to eating healthier because that made running easier (also less "food hangovers" from eating garbage); kept reducing drinking until I just stopped, and now don't see any reason to ever drink again (I feel I actually have energy and focus to Do Things on evenings and weekends - without drinking, weekends feel like they go on forever).

I've always tended to be a "meh" person. This hasn't turned me into like a type A extrovert or anything, but even when I feel down I don't feel that down anymore, and it doesn't go on for as long. My baseline mood is just a bit higher.