I have arthritis in both knees.
I train a lot on a hydraulic resistance trainer. Up to 50 miles/day and up to 100 miles/day road biking.
Upper body exercise is done with rubber bands every morning. About 15-30 minutes.
Treadmill is OK with a slow jog at 4 MPH and 6% incline.
Hiking at 4 MPH for up to 12 miles/day.
The above routines seem to work and my arthritis has not gone worse or better.

I do have to be careful. Stretching muscles or joints result in lasting pain. Biking in too big a gear will cause pain. Jogging on pavement will disable me for several days.