z= gives you spell suggestions for the word under the cursor. Prefixing it with a number auto-selects one of those suggestions. That means 1z= will automatically fix the word under the cursor by applying the most likely correction.
Since 1z= is a bit cumbersome to type, I remapped it to something like za (for consistency with zg to add a word to your spellcheck dictionary). A nice workflow for spellchecking is to use ]s to go the next misspelling, and za to autofix it.
1vim.keymap.set("n", "za", "1z=") -- fix word under cursor
1z= also works when spell is off.
Bonus: You could even create a small macro with ]s and 1z= to autofix all misspellings in a given file.