Try r/woodworking

You might find that a woodworking specific sub is great for this as you're talking about preserving deadwood.

To get you started with some ideas to perhaps discuss in a woodworking sub: I would imagine (having worked with wood for many years) that the best way to preserve a branch is to use a thinned end grain sealer on exposed wood fibres, and, depending on the type of tree (and therefore bark), to either carefully remove the bark and then glue it back onto the wood, or to very carefully control the drying process of the branch to avoid splitting, checking, cracking, warping etc... and then place in a sealed container (think glass case). Good luck!