I had the same issue. Bought a bike out of town and didn’t realize my hanging rack wouldn’t work. I had just bought the rack so I didn’t want it to go to waste so I bought a cross bar adapter (attaches the seat tube to the handlebar stem). Allows new geometry to be able to be hung on hanging racks. Just got to look out for clearance issues, mine is on a lifted jeep so I don’t have that issue, but if I ride with my girlfriend, I have to take off my wheels if I don’t want them to be vulnerable to hitting the pavement on bumps or something. I’m using the “Saris Bike Beam” and it’s $42 on Amazon.
I will be getting a 1up tray style when the funds allow it, but I’ve been using a cross bar for a few years now with no issues.