Based on the answers, varnish is mainly a canvas/inkjet product, and there’s no evidence here that it’s suitable for Kodak Endura photographic paper. Since the manufacturer only tested its product on canvas inkjet prints, using it on lab photo paper would be experimental and risky.

One answer notes that older darkroom prints were sometimes treated with wax polishes to slightly protect the emulsion and deepen blacks. A beeswax-based picture varnish/wax was mentioned for classic baryta prints, but the responder had not tried it on inkjet or on your type of Kodak print.

So the safest conclusion is: there is no clearly supported varnish recommendation here for Kodak Endura prints. If you want protection without glass, coatings used for canvas should not be assumed compatible with photographic paper, and wax/varnish options for traditional prints don’t confirm suitability for modern lab prints.

If preservation matters, test only on spare prints first and get guidance from the print lab or paper manufacturer before applying any coating.