You can now quickly join a meeting as a guest without signing into a personal or work Google account or creating a new Google account. This functionality already exists for meetings on the web and, by expanding to mobile, guests now have greater flexibility for joining Meet meetings on the go. 

To join as a guest, you need to be on the Calendar invite for the meeting or have been provided the meeting code or the meeting link beforehand. Before you join the meeting, you’ll be prompted to enter your name and “knock” (aka ask to join the meeting) to be admitted. Once a meeting host or co-host accepts your knock, you’ll jump right into the meeting.

Source: Google Workspace Updates