Things like "ok, we can't use one drive - need a different tool," "can't use Sharepoint, need to use a different tool," and so on.
The market is there. RHEL and similar are well established.
In order to make this a "we should do this" either government IT funding needs to be significantly increased (that is difficult in the current political climate in most places) or the support offerings and staff needed for the average user (using Windows, Sharepoint, Word, Excel, Teams, and Project) needs to be competitive with the pricing that Microsoft offers.
That should be "simple" - make a company that offers the same level of support as Microsoft does for a packaged suite of software that includes easy installations, appropriately locked down desktops, call center, and so on.
And if that can't be found at the same price that Microsoft offers - then we return to the "increase government funding."
Saying "we should outlaw government spending on closed source" misses a lot of the tools out there that are needed to keep things running. Is there a FOSS (with support contracts for the stack) alternative to Cerner or Epic? SAP? ArcGIS? And that's not even getting deep at all into the niche SaaS tools that some pieces use for specific problems.
The market is there and state and local governments would likely jump at the opportunity to switch if there's a company that can offer the same functional stack with the same support for the same price or cheaper built on top of FOSS. Otherwise... persuade those state and local governments to staff up to the necessary levels to be able to hire people able to customize and support the FOSS to fit their needs and be prepared to financially support that decision.