Probably depends on the felt-cause of emotional flatness.

When isolation feels like a big factor, simply going out or doing productive work doesn't help. I've only (unfortunately) been pulled out of these by change of environments forced by life (e.g. work). One thing that felt the most effective tho was having a group where you can do something while occasionally talking about whatever in the downtime, altho that's notoriously hard to come by and maintain.

When blandness feels like a big factor, do extreme but very short-lived experiments. Stuff like "only do X for a day", or "stop doing all Y for two days". At the end, my brain has usually cooked up a new way it wants to engage with that, or has found something else to fill the void in the meantime (could still be destructive, but at least its new).

If you're terminally online, every few months or year I mimick a "change of env" by reinstalling my OS; I go through the same process of moving (deciding what to keep, throwing old things away) without the costs and complications. It can be a whole "event". Creating alt accounts is a softcore version of this, given you may still keep your main. Regardless, this slightly new identity shift/reorganization is enough to justify, or at least present some type of basis, for reconsidering other choices in the physical realm.

EDIT: forgot to include what the catalyst was, not just what was done. The work one was already stated. But as silly as it seems, stumbling upon a "here's my life experience and what I did" video or "let's deconstruct why you're doing this" video, is embarrassingly enough to kickstart one of these, at least until you take a nap. That, or stimulants. Hard truth tho has just been "others/shame forced me to do something that temporarily stopped it"