Help Notifications on phone remain, even if I view the content on another device

Phone: S21 Ultra
Carrier: Verizon, 5G

I recently upgraded from the S9+, which was also on Verizon. It was a 4G LTE phone at the time. And it had a neat feature where if I had a push notification for email or facebook messenger, it would clear that notification if I opened my email or facebook messenger on my PC, without me having to unlock my phone. As soon as I open gmail/messenger, the notification disappears on my phone. This was really convenient because it prevented me from seeing notifications for things I already knew about.

However, ever since I upgraded to my S21 Ultra (which is a 5G phone), it doesn't do that anymore. If I get a notification for an email and I open that email on my PC, the notification icon stays on my phone. Its really annoying, because I'll look at my phone and see icons, so I stop what I'm doing and look. But then see they're old notifications.

I've also noticed that notifications take like a full 20 second before they hit my phone, behind getting the notification when at a PC. So, imagine I have my phone next to me at the PC. My messenger tab in chrome dings with a notification, but I don't click it. 20 ish seconds later, that same notification hits my phone. It used to be a few seconds with my S9+.

I am confident that it is not an app problem; the only thing I changed was the phone. I didn't modify settings on any of my apps. That being said, I still reinstalled messenger, and it didn't fix the problem.

Maybe its because 5G is a different beast? I'm not paying for the plan where my traffic is prioritized, could that be it? I have no idea what the correct thing to search on google would be, I've been blindly shooting in the dark for months.