KDE Connect has been mentioned before. You can supplement this and other tools by using a VPN so that both endpoints can see each other even if the underlying network does not allow this. My preferred solutions are Tailscale (managed, cloud-based) or Headscale (for self-hosting).
My setup is smaller, but when my venerable old router died about a year ago, I acquired an Asus TUF-AX3000_V2 where I installed FreshTomato. One can login via SSH and dump all settings for backup. Likewise, individual or all settings can be done on the command line instead of the GUI. I have a script on my computer that reads CSV files with MAC addresses and more to apply changes in an automated way.