Got an old DSLR that output HDMI. Got a MBP M1. Got a USBC hub with HDMI port.
Can I output from the DSLR into the hub and and transfer it and capture inside the MBP via USB-C port?
The MBP's HDMI port is only an output. So no, you won't be able to capture it that way. It requires special equipment to capture through HDMI (like this one for example).
What is it exactly you want to do?