Saw a TikTok a few weeks ago talking about pickled grapes, so I decided to give it a shot. Dissolved sugar in water, once cooled I mixed in apple cider vinegar and pickling spices. Then poured it over a quart of washed red seedless grapes topped with a couple slices of red onion. It went into the fridge for a week, but I got impatient after 4 days and ate almost the entire jar in one sitting.
The tiktoker did a follow up video using white vinegar, salt, and mint. This batch was not very good, despite using less salt than he did they were too salty.
The recipe (I posted it a few minutes ago) called for seedless red grapes. I would guess you could use seeded grapes, and eat them as you normally would a seeded grape.