what is my risk of asbestos exposure due to a previous drywall work?
if it was an interior wall, there would likely be no insulation. Even if it was insulated for some odd reason, most wool-type insulation (the kind you'd expect to find in walls) does not contain asbestos. The main form of asbestos tainted insulation in most single family homes is probably vermiculite, and you would generally not find any large amounts of that in wall voids (it was used as loose fill attic insulation; I have a bunch in the ceiling over my head). It was banned in 1990, and to my knowledge was rarely if ever used during new construction, so the odds of finding it in a house that was built in 1987 are slim to none.
As far as the joint compound goes, if the house was constructed in 1987 then it is almost certainly not a type that contained asbestos. I think that stuff was discontinued in the 1970's.
Even in the very unlikely event that there was actually asbestos present, the level of exposure you would have had from some light drywall work is extremely small. The risk of illness is proportional to the level and duration of the exposure, so your risk is very low even in the worst case scenario. If you are looking for things to worry about, I'd probably rank rabid raccoons and murder hornets higher on the list. And as you mentioned, there's not a thing you can do about it now anyways, so you might as well just enjoy life for whatever time you do have left.