This looks like a comprehensive GUI based architecture/design tool which outputs code, runs it and also re-integrates drift and allows for dynamic, realtime changes between users/teams.
Last i checked TFCloud did not do all of this... it still relied on users managing the code themselves but provided features derived from the state storage and execution.
If i wanted to move away from TFCloud i'd take a look at the list of supporters behind OpenTofu
https://opentofu.org/supporters/ they are are the ones directly affected by the legal manoeuvres which make terraform unviable for them to run on their customers behalf.
But please let me know what you find in your analysis of brainboard... it seems really cool.