Passport with Mac Time Machine

I bought 2 WD Passports. I want to use them as time Machine backups on Macbook. I have reformatted both to AFPS, which is required for Mac with TM. When opened for the first time, TM should ask if I want to use it as a backup disk; it does not ask. I can copy Mac files into the Passport. I have spent a lot of time trying options, including several hours with Apple Support, nothing works.

Hi @wjf,

Please refer to the article Acronis True Image for Western Digital: File Backup and Restore to a WD DAS:
https://support-en.wd.com/app/answers/detail/a_id/30022

If further assistance is needed, please open a case with our support team at the following:
https://support-en.wd.com/app/askweb