Back in 2012, at age 55, I had a complete thickness full tear of my rotator cuff. When they did an MRI that finally figured that out the surgeons I went to said "Oooh, and there is retraction, too" which meant the torn ends had pulled back, making repair even harder. Oh, and in compensating I had sawn through my biceps muscle (a common thing) and that had to be sewn up, too.
Successful surgery, got back full range of motion but not full strength, and 9 years later I'm going miles of outdoor (mostly road) cycling each year.
The surgeon I chose told me something that stayed with me. He said "What I did was essentially sew two pieces of pinky-thick spaghetti back together - pretty easy for that to tear out. But over time, scar tissue builds up and two things happen: (1) you will probably have a "noisy" shoulder (I do); and (2) the scar tissue makes the connection much stronger."
Then, the part that stuck with me: "This coming year is the only time that scar tissue has a chance of forming - you have all the years after that to cycle. And, the most common way for the surgery to fail is if you fall and that arm/shoulder takes the weight of the fall." He said it wasn't likely I was going to hit a bump in the road and damage it - but if that bump threw me off the bike, different story. Mountain biking may be a different story, I'd ask the surgeon.
For a year, I only did indoor cycling or rail trail riding with my wife. Since then, many miles of cycling with one road rash incident that didn't cause damage to the repair.
So, my advice is err on the side of caution in choosing activities/routes/trails where you might end up on the ground and ask if you need to worry about the arm/handlebar shock load.