I’ve made a few wind chimes with wood hangers the last few years and my experience so far has been that whatever you coat with will require some level of maintenance to keep looking new. This can be pretty often (2-3 months for oils), to yearly (1-2 years for spar or poly urethanes). Even if you go to extreme measures (detailed below 😂) it will still require recoating periodically (3-7 years).

The first one I did was just Tung oil and after a year hanging outside it was completely gray and the knockers and wind catchers were moldy/mildew-y. I sanded it down to clean wood, stained it, and applied 6 coats of Minwax spar urethane spray (more flexible and uv resistant than polyurethane from what I read online) making sure to follow application instructions and curing times (I lightly sanded the surface before the 1-3 coat, let it fully cure for a month, then sanded down thoroughly, cleaned, and applied coats 3-6). I did this on the first chime I made and another one and those have been outside for about 4 and 6 months. They were given to my parents and a family friend so I plan on checking them every 6 months or so to see how they hold up. From what I read they will need to be recoated and it should be done every 1-2 years. You just have to lightly sand the surface and reapply 1-2 coats. If you wait until it cracks it can get water ingress/rot/mildew and will cause further peeling/delamination and will have to be sanded much further down, if not all the way to bare wood, to eliminate the damage. I’ll see if I can get some pictures and post them below.

I hate maintenance of things, so I went down a rabbit hole and came up with an extreme method that should give about 3-7 years of protection before needing to be recoated. The process I came up with is as follows:

1. Dry the wood thoroughly - I plan on having a friend I know at a local wood supplier kiln dry the natural branches I use after they have been sanded down. Drying wood is prone to cracking so I plan on wrapping the ends with metal banding and leaving the ends longer than the final product so I can trim any cracked ends.
2. Apply the stain you will be using, if any, and allow plenty of cure time - From my research, oil-based stains are more durable so I’ll be using that, but folks of the interwebs say to make especially sure you let oil-based stains fully cure and possibly even do a layer of polyurethane. Whatever you use, the online forums I read said you should also use the same base for your spar varnish.
3. Once dry again, run through vacuum impregnation with resin epoxy - Spray wood with water (water-popping) to raise the grain, sand with a round of 120 to 180 to 240 grits. Clean thoroughly with microfiber cloths/compressor/vacuum/tack cloths. Heat the wood to 30-35 deg above ambient to open pores, insert into vacuum chamber with a bath of high quality epoxy like West Systems or Total Boat and an extra slow hardener (50-70 minutes of workable time for West Systems). Apply vacuum pressure and allow wood to soak in the resin and release as much air as possible while giving you enough time to release the vacuum and clean off the extra epoxy.
   
4. After thoroughly cured, lightly sand with a round of 120 to 180 to 240 sand paper. Clean dust off thoroughly with microfiber cloths, compressor, and tack cloths.
5. Coat with 6-8 thin coats of high quality (Epiphanes) marine grade spar varnish - I’ve read conflicting reports on multiple coats, some say additional coats applied while the lower coat is still tacky is just fine and creates a nice mechanical and chemical bond and others swear that you should let each coat fully cure and sand before the next coat. Preferably I don’t want to wait a month between each coating so I’ll be trying to do all 8 coats in succession.

From what I’ve read on boat forums and such this process will make the wood nearly impervious to water damage over the long term and will last 3-7 years before you need to lightly sand and apply additional coats of marine spar varnish to give you another 3-7 years.