Very similar to @jimblock I opted to use a short TB4 cable to go from my old M1P my new M4P 14" too since I expected highest throughput from that.
I wasn’t around to follow the details, but when I came back after a while it had transferred all ~300 GB and claimed it had done so over wifi. Now my home wifi is fast (~500 Mbps over final gen AirPort Extreme) but I doubt it’s that fast.
I never really understood what my options are and although MA insisted on connecting to a wifi, it never explicitly asked me if I wanted to make use of the direct TB4 connection. I know it’s a quality cable because I use it to run 3.2 GB/s data to/from a fast external NVMe SSD all the time. I also know it recognized the TB4 cable connection because the new Mac later showed it had a TB4-based Gigabit interface defined in its network settings.
There has been some debate as to what type of connections MA supports. It has been claimed that MA on initial setup does not offer the same options as MA on top of an existing installation. But various sources seem to contradict each other and Apple’s documentation is vague. Clear as mud. 
I have no complaints about the process really. It would be nice if users could force a certain transfer mode, but that’s not usually the way Apple likes to do things.
If I’d want to be 100% sure I’ll be transferring at the maximum speed possible, next time I’ll just connect my old Mac’s final TM backup via TB4 to the new Mac and migrate from that. Should migrate just the same as direct Mac to Mac, but the 40 Gbps of TB4 will certainly beat out the 0.5 Gbps of my wifi. Obviously if your TM backup is on a slow HDD (1 Gbps) the conduit or protocol isn’t the bottleneck and you’d be better off going direct from old to new Mac over whatever MA chooses.