There are extensions on Firefox for Android that do this for you. I think it’s very accessible.

I have a Keychron K3 Pro keyboard that can be programmed with VIA and I’m more than happy with it.

My mouse is a VAXEE Outset Wireless. This doesn’t need any software to change DPI / polling rate etc. All of it can be done by pressing buttons on the underside of the mouse. It works very reliably.