More the Mac mini, which had built in 10G as an option in prior generations.

For laptops, you can use an external dongle. It has its uses, like for a NAS on a 10G network for video or other data-intense work.

I have about 20TB of data on several external hard disks / nas / machines. Due to some disks failures I had to move these data and believe me I wish I had 10GB Ethernet so that transfers don't take literally days.

Well, the older Mini that the M1 Mini replaces has 10Gb Ethernet. That being said, there's no modern MacBook that has 10Gb Ethernet anyways. Cannot that port be added over Thunderbolt 3/USB 4 based dongle?

It makes a huge difference for networked storage. For some rough equivalency (ignoring seek times, but also ignoring tcp overheads etc, total spherical cow territory)

- An 8x cdrom narrowly beats 10meg ethernet.

- 1x dvdrom narrowly beats 100meg ethernet.

- ATA133 narrowly beats 1gbit ethernet.

Original SATA is 1.5gbit, so 1Gbit ether bottlenecks us to 1999 storage speeds.

Ethernet ≠ Internet