This is a ceiling support/holder for LED strips of 12x6 mm (with the lighting element being on the short side). The hole in the support is only 10x6mm to make the translucent part being fully visible.

It's meant to hold that kind of LED strip

Fit is tight, the LED strip won't move at all once inserted.

Holders each have one screw spot but you only need to screw around one in 3 for a tight ceiling fit if you glue holders together in groups of 3 (I used cyanoacrylate glue sold as “superglue” or “instant glue” - with PETG it's far from being instant though).

Print with supports, I used PETG with 10% infill but I'd recommend using a less translucent plastic than I did and use something matte instead (or paint it with your wall/ceiling color) since the white on mine looks grey-ish in low light conditions.

I think PLA is fine, the LED strip doesn't seem to heat much, but I'll let you confirm that in comments eventually.