As of Craft 3.5, the useProjectConfig setting is deprecated, and Craft ignores the setting. That makes updating to 3.5 a great time to start using Project Config using the steps below.

<aside> 💡 These are the notes I use for my own projects, and may not be 100% accurate for yours.

</aside>

• [ ] Download the production database to the local site with Craft Scripts' scripts/pull_db.sh
• [ ] Create a backup of the database with Craft Scripts: scripts/backup_db.sh
• [ ] If composer.json is referring to an older version of craft, update it to "craftcms/cms": "^3.5.0",
• [ ] Run composer update
• [ ] If you're running Composer 2, and the server hasn't yet been updated to that, run rm -rf vendor then composer update again. This will create a composer.lock file that's compatible with both Composer 1 and 2.
• [ ] Visit the control panel to complete the update
• [ ] Generate an $APP_ID with ./craft setup/app-id. See Cache Configuration.
• [ ] Take the values from Settings > Email and put them in .env as $ENVIRONMENT_VARIABLES
• [ ] In the control panel, Update Settings > Email to use the .env variables you created
• [ ] Update the .env file on staging and production with the new email settings and generate a unique APP_ID for each environment
• [ ] Read the Project Config docs and Upgrading to 3.5 Project Config Workflow
• [ ] Optional: Add "config/project": true, to .vscode/settings.json to remove the Project Config files from your Visual Studio Code project
• [ ] Remove "useProjectConfig" => false from config/general.php if it's in there
• [ ] In config/general.php, add use craft\\helpers\\App; above return [, then change getenv('SECURITY_KEY') to App::env('SECURITY_KEY') (or update your general.php file to match the new things added in the latest default Craft install)
• [ ] In config/general.php, add this to the staging and production environment settings: 'allowAdminChanges' => false,
• [ ] You can't access Settings on staging / production after that, so remove storage/rebrand from .gitignore so that it deploys the site login logo and icon with git add storage/rebrand -f