[Samsung Galaxy S20 / S20+ / S20 Ultra Questions & ] CharlzO_2000:
I actually just came back to add more confusion to my post, but I'll answer above as best as I can:

I don't have Verizon for home service, but Verizon Wireless for my cell. My S20 Ultra was purchased directly through the store, with all Verizon updates installed and current. My home internet is new 50/50 Fiber internet, which was just deployed to the area about 8-9 months ago. I was the first person on the loop to be installed, and it runs fine. I could up the speed if I wanted, but have no need for more. It's new cable from the unit in the field, up to the road, and new drop to the house and new equipment. From that standpoint, everything has been rock solid and works fine. I certainly am not letting them off the hook (or, wasn't until five minutes ago) for what might be a setting somewhere between points.

However, during some more testing, someone mentioned they had an issue with WiFi calling not working. So I did more testing with my S20 Ultra. Turns out, WiFi calling isn't even working at all on my device. I can place it in airplane mode (so it doesn't see my Network Extender), enable wifi, and no matter what I try to do, it will not recognize WiFi for calling purposes. I can enable it fine, it shows enabled, I can restart and toggle all day long. But the moment I try to make a call that way, it tells me I must turn off Airplane mode to make a call. This is in spite of the phone having wifi calling enabled, with WiFi set as the preferred call type in it's settings. This is full wifi from within feet of the router. On a whim though, I took out my SIM card and put it back in my S10 5G sitting in it's box. Calling works perfectly, on both wifi calling, and the network extender. So all that did was confuse me more.

I have an S9+ that doesn't work. I have an iPhone 11 Max that doesn't work. I have an S20 Ultra that doesn't work. But an S10 5G that does. It's the only phone I've found in the house so far that I can make or receive calls from/to, and be heard on the other end. All the other phones, connected to the same wifi and the same network extender all suffer from the same thing. At this point, I've basically hit a wall and am ready to throw in the towel. I was ready to spend another evening messing with the modem until my S10 worked perfectly. It worked on the extender fine. I put it to Airplane mode, enabled wifi calling, and within twenty seconds it registered an outgoing call to my house as a wifi call, completed, and could hear fine. A bunch of coincidences all at once. My fiber internet came with a new modem, though the same model that my regular DSL used prior - when everything worked fine. This new one is configured exactly the same, I kept the wifi configuration exactly the same as before to eliminate having to set a dozen devices back up. So I thought that change still somehow did the phones in, as it was shortly after that I realized that they weren't working right. But then the S10 connected just fine, using the same new modem and everything.

Pretty sure I just live in the bermuda triangle of befuddlement here. I'm just going to abandon trying to figure it out, and go back to just calling back anyone that tries calling, from my home phone instead.