I do not think a 1/4” will make a difference.

I have a vacation place in a high humidity, low temperature area. I use louver doors. Temps in the 50’s, humidity in the 90’s.

What is an air flow louver?

I have used air circulation vents, are they the same. I am in the USA, CA. Where are you?

kudzu9 - can you recommend louvers/vents that will look nice. The closet door is visible from the main area of the basement, I would like to have vents that look nice. the few that I have seen online/Home Dept didn't look nice..

glfjjf-

Take a look on Amazon. They have a variety of wooden grates/louvers, like this one:

Oak grate

Or use a decorative metal floor register which comes in a variety of finishes, and which you could mount in a door by drilling a couple of holes and screwing it in place. For example:

Floor register

Maybe use decorative metal sheet. Cut hole in door, cut metal to fit (spray paint if wanted), frame out with simple wood strips.

https://www.lowes.com/pd/M-D-12-in-x-2-ft-Aluminum-Sheet-Metal/999959591

There are a bunch of different designs.

Without dehumidification, louvers or undercuts won't help. If the closet adjoins an un-insulated foundation wall or has an un-insulated floor, no help either.

Keep closet doors open when not using the basement.