I had this exact same issue on my iPhone 8Plus. I removed my VPN and removed McAfee security app from my phone, and now everything seems to function normally, with the occasional drop call. I remember reading further down this thread, that apparently ios14 and VPNs don't work well together at the moment? Not sure how true it is, but I can definitely confirm that after removing McAfee and the McAfee VPN on my phone the connectivity issues have improved 90%. I still lose signal occasionally and my 4g won't load at times, however, at least now I can get some calls/texts through to my phone and stream music when out and about. Hope this helps.

Same issue here for past 2 months on IPhone 8plus IOS14.3. I removed my VPN and the McAfee security app from my phone and now the 4g work intermittently. I find that every time I want to use 4g I need to toggle AirPlane mode on and off just for it to connect. It will usually only load like 1 webpage and then I have to toggle airplane mode again to restart the connection. Phone calls also frequently drop out. I change carriers twice, thinking it was them, but my carrier sims works perfectly in other phones. However on my iPhone it continually shows 4bars of signal until I make a call or connect to 4g; then it drops to like 1 bar -> SOS -> no network -> back to 1 bar and so forth. Really annoying.

100% Same issue here. I have 3 IOS devices in my home; 2 iPhone 8 Plus (Me & My Father) and an iPhone X (Mother). Ever since updating to IOS 14 on my phone (iPhone 8 plus) and my mother's phone (iPhone x), both of us receive low to no signal. The status bar will show full reception until you try to make a call or connect to cellular data. The calls will continually drop out or fail. Text messages do not always send and the 4g connection will always time out. The only solution I have found is Toggeling Airplay mode on and off and then trying to make a call or connecting to cellular. However, this solution only lasts for about 1min and then the signal drops out again and the phone will either display SOS or No Service. I've had this issue since late November 2020. Initially, I assumed it was my carrier (Optus at the time), so I switched to Vodafone. However, the same issue occurred. Then once again I switched my provider to Catch, But again the exact same issue. After about 1 week with a new carrier, the issue starts again, which is ridiculous. The apple technicians at the Apple store don't know what the issue is and try and dodge it at all costs; saying that it must be a hardware issue, which I find difficult to believe - I mean two phones, having the exact same issue after an update to a new IOS surely sound more or less like an OS issue. My father on the other had A iPhone 8 Plus running ios 13.7, and the network runs perfect!!, I even switch my sim with his phone and the network works fine. When I put his sim in my phone (Running IOS14.4) the same issue with drop calls and reception issues happen again. I have tried all the troubleshooting techniques, but nothing works. I have to do the 'reset network' almost daily, but still, nothing happens. As mentioned before the only solution I have found that works reliability (albeit only for like 1-5mins) is the Airplay mode technique. I've heard that some people are suffering from this issue for over 5months, which is ridiculous. I hope apple provides a patch update soon.