Six of the ten lessons are the same whichever platform you use. Four are not, and they are the four that matter most in practice: where the files live, who owns them, how you build the front door, and which assistant answers questions.
Pick the one your team already has. You are not choosing a platform here, you are telling the course which one you are on so it stops showing you the other one's screens.
If you are genuinely not sure: look at your work email. If it opens in Gmail, you are on Google Workspace. If it opens in Outlook, you are almost certainly on Microsoft 365.
You can switch later. There is a link on every lesson.