How to find all reactions on a cantilever

As it is indeterminate to one degree. So we need one compatibility equation. That equation is defection at the propped end is zero.

Method 1-Maxwell's method of Superposition. Find the deflection due to uvl at propped end, find the deflection due to reaction R at the propped end.

Subtract both and put equal to zero. You will get the reaction. This the most simple way of getting answer in one line.

Method-2 You can also try Strain Energy method, and put the first derivative of energy wrt applied reaction at propped equal to zero. You will get the same answer.

Method-3 Using Mohr's Method that is Moment Area method, find the deflection independently at the propped end, first by applying uvl, then by reaction R only, put the difference of both equal to zero.