How to recover an InDesign file on a Mac

Right after a crash

Restart InDesign. It checks its recovery folder and reopens the documents that were open, with the changes it saved.
The title bar shows [Recovered] after the file name.
Choose File > Save As, pick a location and a new name, and click Save.

To use the version on disk instead, close without saving, or choose File > Revert. Revert throws away everything not saved, so Save As first if you're unsure.

Where the recovery folder is

By default in ~/Library/Caches/Adobe InDesign/<version>/<language>/InDesign Recovery. To be sure, check InDesign > Settings > File Handling, under Document Recovery Data. Click Choose there to move it.

The files in it are encrypted. You can't open them yourself or with another app. Only InDesign reads them, on restart.

Where InDesign keeps its document recovery data on a Mac.

If InDesign crashes every time it starts

A damaged recovery file can make InDesign crash while recovering it. Quit InDesign, move the files out of the InDesign Recovery folder to your Desktop, and start it again. Work on a copy of a damaged document, never the original.

A document you saved over

InDesign keeps one version of a local .indd: the last save. Restore an older one from Time Machine: open its folder, open Time Machine, go back, select the file and click Restore. If macOS asks, choose Keep Both. InDesign cloud documents have their own version history.

The faster way: Caretaker

Caretaker's Studio shows when each project was last copied to another drive and makes a verified copy in one click, so an overwritten or lost file has a second home. It also lists the fonts an .indd file names that aren't on this Mac.

Caretaker's Studio: a project's size, what it uses, its backup, and the caches and renders it can clear.

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Questions

Does InDesign autosave?

Not to your file. It saves changes to a recovery folder about once a minute and uses them only after a crash.

Can I open files from the InDesign Recovery folder?

No. Adobe says they're encrypted. Restart InDesign and it recovers them itself.