I'm having a similar issue with my iPhone 11, after doing the iOS 14.5.1 update just two days ago. My phone doesn't connect with my phone or WIFI. I can't connect with AirDrop either. I get completely random spurts of connectivity throughout the day with a burst of FB, Telegram, and WhatsApp messages popping up out of nowhere or updates to the weather on my Apple Watch and phone.
I tried the "Apple Recommended" solutions as well as a more thorough one I found here: https://www.ikream.com/iphone-11-pro-that-has-no-internet-access-but-connected-to-wi-fi-network-38605up to resetting all of my settings. As far as I can surmise, the problem isn't with the router or the mobile ISP. It's with the phone itself. Before proceeding with the drastic step of erasing my phone completely and starting from scratch, I thought it best to research if this glitch had some association with the new iOS.
From what I've found, that actually looks to be the case. My question now is, "How soon will iOS 14.5.2 be released to finally (I hope and pray🙏🏾) resolve this issue?"
In the meantime, the only SMALL solution I found was resetting my phone by pressing buttons in this sequence: Volume UP, Volume DOWN, and holding the Power Button till seeing the apple. Every time I do so, I have 3-5 AMAZING seconds😍 of connectivity before it shuts off. So, as soon as the phone turns back and I see the "Home" screen, I race 🏃🏾♂️💨 to check whatever updates there might be in my messages or emails before things shut off again. Then, I repeat until I get all of my updates.🙄
LASTLY, I know don't if this helps to share. But early this morning (Kyiv, Ukraine time), I had a brief restoration of the internet and wifi access to my phone. It lasted for about 5 hours before returning to its previous "bipolar" state.