This isn't a Windows problem. The OP would experience the same problem on Linux. I've run into this with SRs. I believe I may have even opened an issue with

This isn't a Windows problem. The OP would experience the same problem on Linux. I've run into this with SRs. I believe I may have even opened an issue with Tailscale to detect when a client is local to an exit and/or provide more fine grained route ingestion depending on where the client is with respect to the SR. But... Again, not a Windows problem. It is easy to fix by just advertising a longer route. But that implies you won't clobber other things. By default a more specific route will be chosen so a longer route advertised on the TS interface won't be selected.