I have crappy ankles and need support on all but the most groomed tracks. I’m an orthopaedic/hand surgeon by trade, and my foot and ankle colleagues threaten me with ligament reconstructions that I want to avoid. Exercises only help so far, I can fall over barefoot at home. The best one is boosting proprioception (knowing where your body parts are) with a rocker board. If your local physiotherapist doesn’t have one, get a 2′ diameter barrel lid and nail half a baseball to the bottom of it – stand and ‘surf’ on that so the muscles of ankle support get used to fast response. It still doesn’t work 100% of the time, if you’re caught by surprise like treading on a rock or slippery sand/mud/ice. The main stabilisers are the Peronei (the meaty bit that sticks out in front of your shin) so exercises like walking on your heels help strengthen these.
I like the Altra Lone Peaks 6 on good quality trails, the low/broad combo is good. Arcteryx Konseal or Acrux ae good on slippery rock, also low.
For serious walking, the only boot I haven’t sprained an ankle in is the Scarpa Wrangell. It ain’t exactly ‘light’, but it’s the lightest thing that does the job (apart from my Asolo TPS plastics!) The Mammut Sapuen is less supportive but 1/3 the weight for less technical terrain.
For multiday walks I tape my ankles, with 1 1/2″ (38mm) non stretch sports tape. I was taught by a physio friend who was a good netballer (women’s basketball), so had plenty of experience of ankles rolled. Shave ankle first (you’ll regret it next week if you don’t!) and use a ‘stirrup’ of tape in a U shape from the medial to lateral side (inside to outside) of the ankle, going about a hand’s breadth above the malleoli (bony lumpy bits). Then a few circumferential tapes to hold the main tape down. The more layers of U tape you use, the more rigid. It’s thinner and easier to fit in a shoe/boot than the commercial braces, and stronger because it’s stuck to you. My favourite is Leukoplast Premium, which is the brown version of the usually white Leukoplast. You need most of a roll of tape to do both ankles, so the Scarpa Wrangell is cheaper over a year or so.
It’s hard to get the tension right, so it doesn’t dig in and cause blisters, but lots of practice helps you get used to the feel of it.
Hiking gaiters don’t really help, back in the 70s I used to have a pair of US Army surplus gaiters of Vietnam War era, they were much stronger and supportive. Haven’t seen that design for decades.
Trekking poles really help, and common sense stuff like not walking while admiring/photographing the view (guilty as charged). Sometimes you just can’t help it, like the rabbit hole hidden in long grass.
I keep thinking about a custom moulded carbon fibre brace to restrict lateral movement but allow flexion/extension, compatible with a lighter shoe. I’ve never seen a commercial one that’s any good.