DirkFirkin Since you are using bridge mode and the router you have connected does not have a 2.5Gbit connection (from the Sunrise modem to your router WAN), I recommend purchasing a suitable new router with a 2.5Gbit WAN connection and at least one 2.5Gbit LAN connection. This will give you 2.5Gbit speed with suitable devices.
If you don’t want to make any investments, I recommend setting your modem to router mode. This will give you at least 1Gbit on two LAN ports at the same time, which is not possible with your router setup.
For your information, although 2.5 Gbit is only available on LAN 4, the total speed without connecting a 2.5 Gbit device is 2.5 Gbit on all LAN ports, which is 1.5 Gbit more than before.
Greetings
Daniele