[htfu]

Hammerspoon can change focus by relative direction. Can be a bit iffy sometimes but between that and HyperSwitch I'm never really at a loss.

[gingerlime]

Thanks. I'm going to try Hammerspoon (and maybe HyperSwitch).

From other comments, it seems like yabai can also handle it, but it seems like a very "hard-core" way, including disabling some Mac security features, and I'm not sure I feel comfortable going that far yet :)