Hotspot prevents data use with the mobile phone?

Have recently had the problem that as soon as I turn on the hotspot of my phone (Huawei P20), I can use the Internet while normal on my laptop, but not on my phone anymore. Have already tried to make me a little smarter on the Internet, but unfortunately find nothing.

Does anyone have an idea?

That was still not possible with my cellphone except for my OP7Pro