I'm barely maintaining my level of fitness these days. I walk the dogs once a day in the mornings going just under a mile weekdays and about 2 miles on weekends (they're small dogs.) If the weather is cool enough I like to take a 2.5 mile walk in the afternoon with the dogs in their stroller at my pace rather than theirs. Or my wife and I will go on a slow bicycle ride that's about 4 to 5 miles.
What motivates me to do the walks or bike rides beyond walking the dogs is that I don't want to have to regain a minimum level of fitness. Also I know that exercising improves my overall feeling of well being and mental fitness.
When I go above and beyond that level of exercise what motivates me is either the pleasure I get from the exercise itself (climbing, hiking, swimming.) Another thing that will motivate me is being able to do something else I enjoy (reading) as I'm exercising. But these things must be easy to fit into my routine in order for me to want to do them. Also some, such as climbing, require other people in order for me to do them. (I know I can boulder by myself, but I don't enjoy that as much as roped climbing.) Another aspect of climbing that motivates me is that when I do belong to a close group of people who climb together are the social connections I maintain while exercising.
Looking toward the future as Covid concerns to away (if they do) and eventually when I retire (probably 4+ years from now) I hope to join a group doing tai chi. I know I could learn to do this by myself with videos, etc but I'm concerned that I won't be doing it correctly and there is a certain level of satisfaction, pleasure and calmness of seeing myself as one of many doing the same thing.
I do hope you find some things that can help you be motivated to get more exercise. If not I hope you're able to get yourself to do the minimum you need to do to maintain your health and well being.