The minimum power requirement for a Thunderbolt port is 15W and as far as I know, that's all the ports on any existing Mac will deliver.
I ended up having a brief conversation with some OWC and then Apple engineers a while back, about this very aspect, because early OWC TB3 SSD's were "incompatible" with 2018 Mac mini's. The initial
theory was that they were dropping out due to power issues, but I think the end result ended up being interference from Wifi of all things.
Anyway - both sides confirmed to me that TB3 ports by spec, deliver 15W to
downstream devices.
The 100W we see quoted everywhere is unrelated to TB3. It's USB-PD, which they also support. This is why a USB-C charge cable is often not TB3 compliant, and supports just USB2.0 speeds - it has the wiring to support PD and basic data transfer but nothing else.
Technically, sure Apple
could make it's Macs USB-C ports a USB-PD power source to provide up to 100W, but I don't think it's even in the realm of likely possibilities.