Any suggestions how I could make these jars more airtight ?

Those lids have a small hole in them that lets air pressure out when you push it on. You wouldnt be able to get the lid on if it was fully airtight, as the air pressure created would want to push it off. You need different jars period

Agreed

If you’re trying not to buy more jars or can’t get them and you have a vacuum sealer I’d just use that over the jars that aren’t working. Don’t pump all the air out and leave it like a bag of chips sealed. Burp and reseal when needed. Good grade stuff should be fine I’d think. I’ve never actually cured like that but I’d choose that over questionable jars after my last jar experiment.

Throw a boveda in the bag even

Wide mouth mason jars, vacuum sealer and this attachment > https://www.amazon.ca/gp/product/B086FRJYHJ/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1

The top of the attachment has a tool for removing the lid without damaging it !

A 1 L jar will hold a loose packed 2 oz. A dozen jars are ~ $15 - 20 depending on the brand.

Cheers

Are you still curing or looking at long term storage. If your still curing you don’t need to vac the jars

You can use a 5-15lt food grade bucket to cure it more evenly then into jars and seal them with a wind of insulating/pvc tape whatever.

I can tell you anyone growing pounds of weed isn't messing around with jars for curing.