Thanks @aibd, the link you provided clarifies some missing information from the installation guides. I have executed the steps exactly like you describe in the section Know your hardware - Samsung twice, both options you describe with the buttons with the timing explained in the video you link there. But it does not boot into TWRP. I have tried too many times and it drives me crazy. Whatever I do, nothing seems to help and I only get the original bootloader and nothing else.
My device is an SM-G960F/DS with Android 10, kernel version 4.9.118-… and security patch of March 2022. I’m stuck with this, any help would be much appreciated!