You may have time to get a crop before your first frost, what variety is it that you are planting and what is their DTM?
If you do plant them make sure you amend the soil prior to planting as the garlic probably used up a lot of nutrients in the soil.

I always grow a few late potatoes, but that's a lot of space to give them. I have had good results reconditioning the soil and sowing rutabagas after garlic harvested in July. With fall crops started in containers, sometimes I sow buckwheat thinly after the garlic comes out, and use it as a nurse crop for the little seedlings.

Garlic and potatoes are compatible, though. This year one of the garlic rows followed last year's potatoes, and I let some of the inevitable volunteer potatoes grow in the middle of the double row of garlic. Both crops did fine, and I recovered planting stock for a fingerling potato I thought I'd lost.

This really isn't a garlic question but a potato question. I often plant garlic where I dug potatoes, but I always have it all planned out. Putting something where garlic was is a no brainer. There are so many crops that can be put in there this time of year!

I like to put potatoes in after my garlic. This year I left two beds fallow in the fall so I could get the potatoes in earlier. I need to start crop rotation here as the virus load seems to be getting higher so I will be leaving some beds empty over the winter every year now.

Greens and herbs do well in my experience. Peas have been a good one, too.

As was said in the prior post, there are plenty of things to try.

I'm also into my fifth season of growing garlic and have followed each harvest with all the same crops as still_kris - potatoes; peas and mustard greens. The peas and mustard greens were intended as cover crops but didn't have the heart to dig them in and ended up letting them grow longer than they should have. The peas were cut back as soon as they started flowering and gently turned over. The mustard greens were seeds I'd saved of rocket, red mustard, mizuna etc that were great as cut and come again salad greens and despite having been cut back with hedge clippers, are still growing away after two recent snowfalls. Read somewhere that the brassica famiy are good soil fumigants.

Last year I put in cucumbers after garlic. You should still have time for a decent crop. This year I'm going to do brassicas. Cabbage and broccoli seeds are already started. Soon I'll plant kohlrabi and gailan as well. If there's any room left in September/October I'll put in some kale.