You can have two devices with a single number but it costs extra and no idea if all providers offer this.
On my Samsung phone I can enable an extreme power savings mode, it disables everything but phone calls/text and makes the screen a very simple black and white affair, perhaps your phone has such a mode?
You could set up an apple watch to only notify you for texts and calls with no other notifications or health information. I would hope smart watches like the new Google one could be configured the same.
For years with regular cellphones before the iPhone was introduced this was an everyday thing.
You would just turn off your smartphone, remove the SIM card and insert it into your previous less-intelligent phone.
Leverage Google Voice maybe?
I pay $5/month for 5G on my Apple Watch and leave my phone at home. The watch is good enough for phone calls, especially with a pair of AirPods.
If that sounds too scary for you, consider leaving your phone in your car while you hang with your friends.
[1] https://taylor.town/leave-your-phone-at-home
You can also disable notifications. My phone only notifies me when I receive phone calls. I manually check it for everything else.
[2] https://taylor.town/extinguish-all-notifications