welcome to the IPFire community, and apologies for the belated reply.
Hm, both options come with disadvantages. If I understood your setup correctly, I would indeed assess that weakening RPF for affected interfaces (should be GREEN only) is the lesser evil than introducing aliases - which would mean touching clients, possibly applications, the server side, etc. pp.
Hello again friends, here again with the same problem, always the same case from the beginning, but here I explain a little better, I have ipfire in a virtual machine, I have 2 network cards, green and red, green This one with the IP 192.168.10.190 and the red one I have with a direct public IP from the router of my ISP provider, I tell you that I am using the IPfire as a proxy in my work, and where the subnets are 192.168.10.0./ 24 192.168.20.0/24 192.168.30.0/24 are being routed and created from a Zyxell, before you had RFC updates everything was going normally, and recently by this same means they gave me a provisional solution with this pair of commands
And almost immediately I had solved the problem of being able to reach the proxy from any subnet, and from the proxy to any subnet too, I have read the RFC everywhere and I cannot find a solution to this, it is worth mentioning that every team within my network and it is in the same subnet of my IPfire 192.168.10.0/24 has no problem are the other subnets.