Probably some kind of beetles or caterpillars. No reason to worry, trees can handle such pretty well. And it will soon stop, when the bugs are full and goes on to the next step in their development

Too far away to be certain but possibly Japanese beetles or linden or basswood leaf miner beetles. Unless a severe infestation (which yours does not appear to be), the effect is more cosmetic than harmful to the tree. It is still well able to photosynthesize and grow normally despite any leaf damage. Treatment is really optional.

Can also be hail damage if only on the upper portions.

If it’s only aesthetic, I’m not going to worry about it. Thanks!

Linden leaves are like candy to many insects. While they tend to get chewed on more than other trees, it's usually not enough to be harmful to the tree. It's cosmetic, like gardengal says. Complete defoliation is another story, but you'd notice if an outbreak of caterpillars was present. And that doesn't happen all that often.

I haven't seen Japanese beetle in my area (north side of the cities) yet this year and usually don't until around the 4th of July or later. And we did have a pretty late spring this year.