I know what a radian is. What’s your point?
It’s a ‘natural’ derived measurement, with no need for a physical or literal standard to represent it.
A ‘degree’ can be anything, of any size value, but because we have a year of 365 days, 360 by the old Roman calendars, we got stuck into 360 degree circles.
We could just have easily used 1000 degrees to a circle, and came up with some easily manipulated numbers. The trigonometry would be the same, jut with a different set of standards.
.........