In my experience, action cam underwater / weatherproof transparent cases have buttons that are quite difficult to use. This seems mostly because they are assembled with no lubricant.
Above, the button in the genuine Sjcam SJ8 has a stainless spring, shaped washer, two 6x2x2mm orings, and a 2.5mm E clip. This pic shows that the thing is assembled dry which makes operating pressure high, and in any event not smooth as the button shaft is not particularly smooth.
The buttons in my SJ4000 case are a little different, the spring bears on a flat acrylic washer which cracks, and I have replaced them successfully with an ordinary 316 M2.5x6mm flat washer.
In both cases, if the orings are not worn and in good condition, a small dab of silicone grease applied between the orings and worked onto the shaft fixes the problem. Avoid excess, you don’t want it oozing out of the button assembly.
The fix works a treat.