I'd say it's not just about spending less time online - the real point is HOW you spend it. I had the same thing: I'd be scrolling and notice my neck was tense, I was breathing faster. The problem isn't really the amount of time but the way these apps deliberately keep you in a rushed state. The constant algorithm feed, the notifications, the comparisons - that actually triggers your stress response.
What helped me: not just less time, but more conscious time. I started asking myself BEFORE opening an app what I'm actually looking for - a specific video, following someone, or just mindlessly scrolling? If it's just mindless, I skip it. And when I am online, I try to consciously notice when that tension kicks in, and then I exit. It's not radical, but it works better than forcing yourself to spend less time overall - because you're just going to do it anyway.
Also helpful: turn off push notifications. Actually turn them off, not just mute them. Sounds like a small thing, but psychologically it makes a huge difference. You're opening the apps on your own terms, not because your phone is pestering you every five minutes. Your body already starts to calm down once that constant interruption is gone.