Consider a block A on top of block B with a coefficient of friction of say 0.3 in between them and the path providing zero resistance (no friction), with the bottom block moving such that its acceleration is 2m/s$^2$. The two blocks move such that the top block shares the acceleration with the bottom block due to the frictional force acting on it being less than the maximum friction value. Now in this instance the top block would have a frictional force of 4N acting on it. Introduce another body C moving at an acceleration of 5m/s$^2$ in the same direction ahead of the first two blocks such that their acceleration relative to body C is now "-3m/s$^2$" since we're factoring in body C being a non inertial frame of reference.
Now if the blocks A and B move with a relative acceleration of "-3" m/s$^2$, the opposing frictional force for the blocks would have a different value (since the blocks are now "moving" with a different acceleration along the negative x axis) which I assume has to be a wrong interpretation since forces are somehow independent of frame of reference but can't fathom how since acceleration isn't. Essentially why wouldn't the value of frictional force change if we factor in pseudo force when changing the entire frame.