[PBondurant]

The issue is not a cable thing. I have experienced the same behaviour on both a 2020 intel MBA and a 2021 M1 Pro; a 10GB/s rated Samsung T5 SSD only connects to either Mac at 5GB/s, despite being rated for 10GB/s. The same SSD (and cables) connects to Linux & Windows boxen at 10GB/s.

Equally, a Crucial X8 SSD rated for the same 10GB/s connects to both Macs at its rated speed.

This behavious has persisted across OS updates since Big Sur.

My current thinking is that there's some undocumented quirks in place in MacOS that scales speeds down with certain USB controllers.

[mlindner]

Sounds pretty clearly like Apple thinks certain devices are non-standards compliant. And just because it works at full speed on Linux & Windows doesn't mean it's standards compliant.

[goosedragons]

Alternatively Apple is not standards compliant. Or it could just be a bug in their driver or controller. Not sure why it makes more sense to assume Apple is doing it right and everyone else wrong.