According to this video and the folks at OWC, each port on the Mac mini is its own bus/controller.
2 minutes, 15 seconds in.
EDIT: Here is the OWC article: https://eshop.macsales.com/blog/68484-thunderbolt-on-the-m1-mac-mini/
2 minutes, 15 seconds in.
EDIT: Here is the OWC article: https://eshop.macsales.com/blog/68484-thunderbolt-on-the-m1-mac-mini/