@Johnnny - The Free Plan supports unlimited team members, so, yes, you can have a unlimited collaborators at the same time.

However, if you are looking to have non-team members edit your boards – at the same time or asynchronously – then you would need the Starter (or Business) Plan where you could use the Visitors feature.

You can compare all plans here → https://help.miro.com/hc/en-us/articles/360017730233