You’re not allowed to store PII in Google Analytics already as per the terms of service:
You will not and will not assist or permit any third party to, pass information to Google that Google could use or recognise as personally identifiable information.
Even if you don't send personal data to Google analytics they store personal data automatically. At least Google Analytics for Firebase store the following identifiers:
Mobile ad IDs
IDFVs/Android IDs
Instance IDs
Analytics App Instance
https://firebase.google.com/support/privacy/
You will not and will not assist or permit any third party to, pass information to Google that Google could use or recognise as personally identifiable information.
https://www.google.com/analytics/terms/us.html , section 7.