Windows: copy %appdata%\Steinberg\Dorico 3.5\keycommands_xy.json (xy is en for English, fr for French etc.)
Mac: copy ~/Library/Application Support/Steinberg/Dorico 3.5/keycommands_xy.json
…or copy the whole folder if you also want to hang onto saved Engraving Options, Notation Options, Layout Options etc.
Note that your AutoSave path is stored within preferences.xml in that folder. If your user account has a different name on the new computer/OS installation, you’ll need to either edit that file in a text editor or just delete the file - it’ll be recreated the next time you launch Dorico.