WiFi speed only a third of the speed at PC

Apps & Core Settings
1

I have a 100 Mbit DSL internet access for my Fritzbox 7530 with WiFi 5. On my PC I have that max. speed via both LAN and WiFi. On my Shiftphone 6mq with iodeOS 6.10 i only have ~ 30 Mbit via WiFi. Both devices are connected with WiFi5, 5GHz 2x2 streams and have very good signal strength. Via LAN the phone also has the max. speed

What can I do do get the full speed on the phone via WiFi, too?

Edit: Sometimes I must de- and reconnect WiFi that the phone connects with 5GHz.

Edit 2: When I connect the phone via the PC hotspot I get ~70Mbit.

2

The only difference between the connection via Router and PC hotspot was WPA3 and WPA2. When I change the security settings of the Router to WPA 2 the phone also gets full speed.

Is this a knows issue with LineageOS/iodeOS/Shiftphone 6mq?