I have a boat with a really pretty mahogany swim platform on the back.
Every year, the same thing. Scrape off the old varnish, refinish. It gets a lot of sun, and dips into the salt and lake water, so I was resigned to this for many years.
I walked into the fiberglass shop, one day. I saw this product called "surfboard resin." I asked about it. An ultra clear polyester resin with UV inhibitors. A light bulb went on.
I took the swim platform completely apart. Sanded it all down to bare wood. Put 3 coats of surfboard resin on it.
That was 7 years ago. It's just now starting to look like a redo is order.
Pretty good test platform though. It gets; bashed with skis, wakeboards, docks, sand, sunscreen, saltwater, sun, you name it.
Mahogany is an oily wood, and this stuff bonded very well.
Check it out, it might work for you.