I think the factor you're missing is that the WiFi and 5G connections may have substantially different latencies to the other person. Going from a lower-latency to a higher-latency connection will always involve audio dropping out and video pausing. And in the opposite direction, it's preferable to skip over a few frames in order to reduce latency, rather than maintain higher latency.

I wonder if you don't see this with cell phones because the latency is generally identical, or if it's just less noticeable with audio than with video? I guess I'd also wonder if cell towers really do hand off without glitches, since there always seem to be glitches when you're driving, but you don't have the slightest idea whether they're from tall buildings or interference or Bluetooth or handoffs or what, or even on your end or the other person's end.

Video conferencing has latency in the 300ms - 1000ms range[1]. The actual network component of that is pretty small. And video conferencing software already has logic for time stretching/compression to handle variable latency - typically they'll speed up or slow down gaps between words and sentences.

[1]: https://www.mdpi.com/2076-3417/12/24/12884

Actually no -- things like FaceTime are more like 90 ms, while other common products like Zoom and Meet are around 150-200. These are minimums with somebody in your own city. This is actually from my own testing in the past, where FaceTime was the clear winner, since Apple cares a lot about latency and is custom written for its own hardware.

But networks absolutely can add major latency, have you never had a slow Zoom call? It's because of congestion building up and radio interference. That's what leads to things like 1,000 ms latency, which makes back and forth conversation very difficult. Perceptible latency issues are always because of the network.

And yes products do time stretching but that's also what people often call glitches because it's very weird.