Is it possible to win K+R vs K+B

Normally, it is a draw.
https://www.chess.com/practice/drills/endgame-fundamentals/e3f7dea6-d397-11eb-b624-9575e021581f
It depends. If you can force your opponents king into the corner of the same color as his bishop then it is winning. In some other rare cases it is also winning and in majority of cases it is a draw.

Most positions are drawn. Ending 6 in Jesus de la Villa's "100 Endgames You Must Know" illustrates the possibility for the side with the R to win.

It's typically a easy draw IF you know what you're doing. There are many ways to lose with the Bishop, usually by chasing it around with the Rook until you can also threaten mate. For the defense, if you are forced to the edge, keep the King near the corner the opposite color of the Bishop so you can use the stalemate defense.