It doesn’t build a .app bundle, which means that it can’t have a proper distribution with appropriate signing &c. that would give it access to various macOS features. It doesn’t have a menu (which _does_ matter).
It doesn’t have a "release" build since May 2020, meaning that the only way to get a meaningful build is to build it yourself (not a big deal, but still).
It doesn’t render fonts correctly, especially on macOS: https://github.com/neovide/neovide/issues/1096, https://github.com/neovide/neovide/issues/589 (although it may be related to how font names are resolved, https://github.com/neovide/neovide/issues/776; https://github.com/neovide/neovide/issues/1057 seems to resolve it), https://github.com/neovide/neovide/issues/851, https://github.com/neovide/neovide/issues/283.
The last appears to be fixed, but the former two are problematic from my perspective as a replacement for MacVim.app.
Why? Because there’s not a _single_ neovim client that is as good as MacVim.app. I paid for Oni2 (I regret that; it’s _not_ a vim replacement). I have contributed code and time to helping a couple of other GUIs fix their issues. But they are all crap compared to MacVim.app.
Until that is fixed, I don’t think that there’s a good reason to consider switching.