Question about Lenovo ThinkVision P27h-10

I bought the Lenovo P27H-10 today and connected it to my MacbookPro 15 from 2019 via Usb C. Everything worked fine, i.e. the screen was displayed on the new monitor. Everything worked fine, i.e. the screen was displayed on the new monitor. I then wanted to connect an external mouse and keyboard to the monitor, but both were not recognised by the Macbook. I then tried plugging a USB stick into the monitor, but it wasn't recognised either. Then again with another mouse and keyboard.... Problem still the same. One mouse lit up at the bottom, but the other one did not. Unfortunately, I could not see whether the keyboards were powered. I suspect that you have to "trust" the monitor under MacOS, but I was never asked. Otherwise, I have no idea what the problem could be. mfg Maik