We understand that the current ability to rearrange tabs does not include files and posts. The feature team is reviewing the ask.
This continues to be on our backlog due to prioritization of other work items. We will update when there is more to share.
The engineering team is continuing to work on adding support for multiple accounts on desktop clients. We will first launch support for 1 work/school account and 1 personal account so users can enjoy Teams for work and personal side-by-side. Windows and MacOS. Support for multiple work accounts is still being worked on and will come at a later date.
You can track status via the roadmap here: https://www.microsoft.com/microsoft-365/roadmap?searchterms=68845.