There are a couple of reasons why recording might be unavailable in Google Meet, and the solution depends on your situation. Here are the common culprits:
Admin restrictions: Meeting recording might be disabled by the administrator of your Google Workspace account. They can enable it in the Google Admin console.
Meeting type: Recordings aren't possible for meetings created on conference room devices or through other processes like Chrome plugins. You need to schedule the meeting in your calendar or ensure a person starts ad-hoc meetings, not a device.
Joining method: Recording is only available on the computer version of Google Meet, not on the mobile app. Additionally, you can't record if you join solely to present, like joining a video conference from a laptop while already in a physical conference room.