The Ladder

In order#

1. :checkhealth — Neovim’s own diagnostic. Missing providers, broken parsers, unmet dependencies, all reported plainly.
2. :Lazy — did a plugin fail to install or load? The UI shows the error per plugin.
3. :Mason — is the language server actually installed and on PATH?
4. Minimal config — start with nvim --clean. If the problem disappears, it is your config, not Neovim.
5. Bisect — comment out half your plugin specs, restart, and narrow it down. Ten minutes of halving beats an hour of staring.

The version question#

:version
:h news

After an upgrade, :h news usually explains exactly what changed and what was removed — a lot of “suddenly broken” is a documented removal.