Miro, the whiteboard tool that I prefer these days, has a few ways to avoid group think in remote workshops:

The Voting feature in Miro allows you to select sticky notes or objects and then have people vote on them. You can set up this vote to be anonymous and as people are voting they don't see the results before the vote is finished.

This is great as people are not biased during the voting process by what they see others doing.

The Private mode in Miro is another good tool that helps keep work in the tool private. It hides the cursor and removes the information of who added the sticky notes.

So people won't see for example, what piece of feedback come from their friend or boss.

Other online whiteboards have similar features, for example Mural also has a voting feature. Just look for them in the documentation of your favorite whiteboard app.