I had a dog with joint problems/arthrosis (GSD, they’re prone). The only things that helped were daily NSAIDs (meloxicam is the go-to for buns), gabapentin as needed, laser treatment and exercise on flat but not hard surfaces (no jumping!).
Nowadays LED light therapy could be a comparatively affordable option for at-home therapy. I think moderator Dana has had some luck with that for elderbuns. Just make sure you get sth that works for fur-clad creatures, many hand held devices for humans only work on bare skin.
Long term meloxicam for buns should be combined with famotidine to protect the stomach lining from the corrosive effects of NSAIDs. Famotidine is an OTC drug for humans, my bun vets prescribe it for short term meloxicam treatment as well (spay/neuters, stasis etc).
I tried lots supplements for my dog. Glucosamine tablets, some combination type horrible-tasting liquid (I tasted it, it was vile 😄🤢, doggy didnt seem to mind though), curcumin, Omega 3 oil etc. I cant say if any of it helped or not. It’s a lot easier to medicate a dog bc they can swallow pills, and liquid meds can be hidden in favorite food. Rabbits are far more picky and also very opinionated 🐰💝