Can my loved one continue to bicycle?

My DH has Alzheimer's - probably moving into the beginning of the moderate stage. He has always been a enthusiastic bicyclist, logging 10 miles several times a week in spring, summer, and fall (but not in our midwest winters!). Two years ago we relocated back to our hometown, and between the effort of moving and adjusting, he hasn't ridden since then, especially since our bikes needed a thorough tune-up, which we just completed. Over the past couple years, his ALZ has progressed, albeit slowly. He's in good physical health overall, but he is moving more slowly and cautiously. He hasn't had any falls, but I have noticed he's more tentative going down the stairs, and also when getting in and out of the car. Still, I was surprised when picking up our bikes from the shop after their tune-up, he couldn't throw his leg over the bar & seat as he has always done. (In fact, the bike shop owner expressed to me later that he was concerned by what he observed.)

I've looked at a step-through "low entry" bike model, which is definitely easier to mount and dismount. (I've also looked at adult tricycles, which were harder to manage than I expected!)

But my primary question is how to best get an assessment of whether he has the necessary balance/coordination to continue riding! Has anyone had experience with this?

(We would always ride together in our small neighborhood or on a nearby bike trail, so it's not about wandering.}