Heads up, it seems it has been limited to a single token for some time indeed (though surely two months ago 3 were allowed), reading this in yesterday’s blog post:
Free users can continue to use their single read, write, delete token and revoke/reissue this as they need.
Also, this is now documented:
You can create 1 access token as part of the Free plan, 5 tokens per the Pro plan, and Unlimited tokens for the Team plan. For more information about a Pro or a Team plan, see Docker Pricing.
And the user interface shows the same thing now:
When using “New Access Token”:
