I made a little ST/Amiga Mouse/Trackball adapter for the Jaguar. You can easily build one yourself as the connections are out there, but if you do not want to do that, I have some extras.
It simply plugs into the Jaguar and then you plug the ST/Amiga mouse or Trackball into it. I have tested it with my multiple Atari ST mice as well as the "Best Trackball" that Best Electronics sells and it works great.
I sell them bare, but I include a 3D printed case "bottom" to them. There is no lid because there is not enough clearance for a proper lid. I will keep working on it, but it really needs to be very thin and it leads to the lid not being very study. You do not really need a case, but it's there is you want it.
I have a page on my website (https://www.thebrewingacademy.com/) for them. They are $20 shipped to the US and $25 shipped anywhere else. If you want multiples, add $15 for each additional. Payment information either via PM or via the website.
These work with Gridrunner (the secret game hidden in Jeff Minter Classics cartridge) and should work with Defender of the Crown (According to Cyrano Jones, and he would be the authority there!).
Again, nothing special, but I had some made for myself and thought others might want them.