1. is this router to be recommended or is the Zyxel NR5101, Wifi6 Indoor Modem Router better?
=> with the Zyxel you can probably set more and have better support as far as firmware updates are concerned. The Huawei things are rather worse in terms of software updates.

2. is 5G sufficient for gaming, streaming, use? (Ping)
=> I use 5G from Sunrise myself and yes streaming gaming works well.

3. are these 5G routers like normal DSL routers? So with these 5G routers you can also make settings like portforwarding or firewall multiple wifi private/guest etc?
=> Portforwarding won't help you because you won't get a public IP from the providers.
Look in the manual of the product then you have your answers.