Hello,
Thanks for contacting us, and sorry for any inconvenience that might have been caused due to that.
It seems you didn’t grant all necessary permissions while connecting Google account with Rank Math.
Please re-connect your Google account with Rank Math by following the steps I’ve mentioned below, without skipping them, and make sure you’ve granted all necessary permissions.
#1 ~ Remove Rank Math’s access from Google
Please remove RankMath’s app from your Google apps permissions:
https://myaccount.google.com/permissions

#2 ~ Re-connect to regenerate auth token from Google
After that, reconnect the Google account again, to regenerate the auth token from Google, by going to WordPress Dashboard > Rank Math > General Settings > Analytics and configure the Search Console and Analytics settings again:

#3 ~ Grant all necessary permissions
Kindly check all necessary checkboxes to allow Rank Math to access some of the Google Services. Please check my screenshot below for reference:

#4 ~ Setup Analytics
Once the above process is done, please follow the URL below to setup Rank Math Analytics properly:
https://rankmath.com/kb/connect-your-google-account/#num-3-connect-to-search-console
After that, please try fetching data from Google Analytics by following the URL below and wait for a while to see if that works for you:
https://rankmath.com/kb/analytics-issues/#scheduled-actions
Let us know how that goes. Looking forward to helping you.
Thank you.