Load mapping file in google play console
- Click on "Releases Overview" in the left panel.
- In the "Latest Releases" section, click on the version for which you want to upload your mapping file
- In the "App Bundles and APKs" section, you would see a row with your added App Bundle or APK.
- Click on the 3 dots menu on it's right end. This would open a menu with an option to "Upload ReTrace mapping file (.txt or .map)"
New instructions are listed here, if anyone else is still looking: https://support.google.com/googleplay/android-developer/answer/9848633?hl=en