[Solved] After trying several troubleshoots this finally helped: go to settings > system > language > regional preferences and set everything to standard. Then force stop the Google and Gboard apps, clear cache and data on both apps. Then activate and set up the Google assistant. Then wait a few minutes as files are being downloaded. Then Assistant Voice Typing should be available.
So, they come to Samsung but not (officially) to older Pixels yet? Good job, Google.