Cheap board, just buy another one!
Shrunken squares
Sorry Herman....From many years past,when i collected acoustic guitars,i knew wood shrinks as it ages. Especially if there are wide humidity swings.....Basically,unless you have a way to control humidity,this can be greatly reduced.....Personally,I have an in room humidifier in my chess/hobby room and use it in colder months.
I don't think the bathroom thing is going to do much.....It's still a nice board.....You can try a little wood filler,if you're inclined and careful.
Just my opinion.....Still a nice board pal. Good luck!

Oooh, echoing @magictwanger here. I'm wondering about your other sets and boards as well. How's the humidity level in their area? I've begun using a wood and grain filler called Aqua Coat on some instruments/projects recently with fairly good results. It isn't likely to hide the gaps however. It would help smooth out the playing surface.

Those squares shrunk before I became owner of the board. No problem with overly dry or humid air where I live. The only thing I "coat" my boards with is wax.
From what I see in the picture Herman.....The woods are really very nice....I love the grain of the dark squares. I figure you can always fill in the separations if it bothers you but, it doesn't seem to have cracks and is a really nice board. Your call how to proceed.
Good luck

Hmmm….ok, probably a silly idea follows … I use this finishing oil on some boards. It’s interesting in that - one coat provides for a semi-matt finish - five coats with a sand in between each - high gloss. The end being a super hard wearing, attractive finish. If this board were mine I’d lightly sand back and try this as the oil/finish … it will fill the gaps with a clear liquid that sets hard … the grain looks good on that board / a finish like this will only enhance it. In short, the gaps are character —- just finish with something that fills that gaps - the board will be smooth and the gaps less obvious.
PS - woodworkers feel free to correct the error of my ways. 😊

As a woodworker, i learned from my new neighbor friend (82 years of experience) that "it ain't effed up until it can't be fixed." 🤣

As a woodworker, i learned from my new neighbor friend (82 years of experience) that "it ain't effed up until it can't be fixed." 🤣
...and countless are the decent things that´s got effed up by some DIY attempt at "fixing". Leave well enough alone are words to live by, at least for us lazy boys...
What´s shown above is the sorry state of one of my favourite chess boards. It´s a foldable board with room to hold a set of pieces. The squares are made of ca 3 mm thick solid wood and, during the many decades that have passed since the making of the board they have dried out and shrunk. What, if nything, shall I do? The board is perfectly serviceable and I have no problem with old gear shoving battle scars, signs of use or patina. Still... If I should leave the board in a corner of my bathroom and forget it for, say, a year, would that help? Or would I risk ruining it completely?