Hi @MrThiemann 

Thanks for posting in our business forum.

So, first, answer your question about static routing: How to configure Static Routing on wireless routers

I am pasting this to help you understand static routing. The static routing is pretty much the same on any router. Since the User Guide has shown the use and steps, you can refer to the User Guide for detailed information.

Second, you seem to know what to do with static routing. So, I've pointed out what you should configure and how by the FAQ or the User Guide. So you should have a basic ideal on "how-to".

But I'll just tell you what should be happening in a normal scenario.

If you are connected like this, then they are in two separate networks. Two NATs are creating two different local area networks, AKA LAN.

MrThiemann wrote

My SkyDSL router has the IP 192.168.1.1 (But I think that doesn't matter at this point)

My TP-Link (192.168.0.1) gave me the IP 192.168.0.115 on my Macbook.

How can I continue to access the Fritzbox network with my laptop? That will have something to do with “static routing”. But I can't get it.

I don't know what I should enter/select for Destination IP, Subnet Mask, Next Hop or Interface.

My setup looks like this.

WAN 1 == SkyDSL router

WAN/LAN 2 == Fritzbox

WAN/LAN 3 == FREE (unoccupied)

WAN/LAN 4 == RE650

LAN 5 == Proxmox

My opinion: static routing is not gonna be helpful anyway to access the Fritzbox network.

A normal scenario:

If your network is like ISP----Router A----PC A & Router B----PC B. From the PC B, you should be able to access the PC A and Router A. You can access their LAN(from Router A) IP addresses, but PC A cannot access PC B unless you port forward.

In your setup, if you want to force certain devices to go through WAN/LAN2 for Internet access, you should use Policy Routing instead of Static Routing.

Same, you still need to port forward, to allow access from Fritzbox to the R480T+. You should use Policy Routing to force traffic to go through WAN/LAN2. But I don't understand what you mean by accessing the Frtizbox network. Policy Routing should do it. Like described above, you should have access to the PC A and Router A if you are connected in that way, which is pretty much the same as your current setup.

If you want others to help you more, you should be more specific. So far, that's my assumption and first reaction.