>Every mini-PC or desktop motherboard that I have bought during the last 10 years had at least one such USB port.
Are you talking about USB 3.2 Gen 2x2 though? Because I've never seen any MiniPC with this port and as for motherboards, I checked my local retailer and only ~15% of currently sold ones have Gen 2x2 (mostly high-end ones).
Most of my mini-PCs have been Intel NUCs (or more recently an ASUS NUC). I also had some Gigabyte and Zotac mini-PCs and a few others from less well-known vendors. IIRC almost all had one such 20 Gb/s USB Type C port, unless they had one or two faster Thunderbolt ports.
With mini-PCs, I frequently use external SSDs, so I certainly used those ports at their full speed.
The only mini-PCs that I had in recent years without such a fast USB port were Arm-CPU based, as those are typically starved in fast peripheral interfaces in comparison with the Intel/AMD CPUs.