u/Dolokan

I know, this question comes a lot, but it doesnt work! I group objects, try to select multiple knots with the select box and everything deselects. I have a Rectangle and a smaller Rectangle inside and want the top right corner of both to be curved in the same amount. I'm going crazy, this should be so easy, but i only find answers from 5 years ago and something seems to have changed. I really appreciate any help.