Hi @David White, welcome to the community! 👋
At the moment, Miro doesn’t provide a way to set a “default team” that opens first. The workspace you see after logging in is usually determined by the last team accessed, but with SSO (single sign-on) the login flow can sometimes redirect you to a particular organization’s team by default.
Since you’ve already cleared cookies and tested, I’d suggest reaching out to Miro Support so they can check if something account-specific is causing the redirect.
Hope that helps clarify things a bit!
@David White / @Eca I made some tweaks to this post.
I noted that as of Monday, August 18, I was constantly being directed to the same team org/team space everything I can came back to my Miro dashboard via a new session (i.e., browser tab or window).
I opened ticket #877653 and it is being investigated. I’ll update this post as I learn more.
Dear Miro Dashboard Product Team: Please expose the team ID dashboard URL, like you so with Spaces. With this in place we could bookmark teams (and this current bug would be less of a nuisance). We could also direct people to a team via a URL rather than explaining to them how to switch team dashboards.
See this Wish List idea post: https://community.miro.com/ideas/ability-to-link-directly-to-a-miro-team-13727
@David White As a workaround, you could open one Space in the team dashboard you visit most often and bookmark it.
Thanks for jumping in, @Robert Johnson, and for linking the related Wish List idea. Really appreciate you raising a ticket and keeping the community updated on this! I will also monitor this case and provide update as soon as I gather the information. 
Update from Miro support:
I'm reaching out to let you know that the team has identified the cause of the issue you reported with the dashboard defaulting to a specific Team. Our engineers are currently working on a solution, and we'll be sure to follow up with you once there are updates!
Update: Support said that a fix was released, but the issue persists for me. Replied to support that not fixed.
I can confirm that the issue persists for me too. Miro always directs me back to the first team in the team list, which is sorted alphabetically.
As of Sunday, September 21 @ 5:00 PM UTC, the issue is resolved for me and I am not being taken back to the last dashboard I visited (Windows 11, Chrome, Edge, and Miro desktop app).
I have replied to my open support ticket to confirm the details.