Outlook is a dumpster fire, and there are perfectly fine alternatives. Very few people actually need the full might of Excel, and you can always RemoteApp it to them, and have the rest use Libre Office. Or heck, provide them with actual tooling better fit for their requirements than Excel.
And in any case, IMHO, "public money, public code". Nothing should be paid for with public money without it being publicly accessible afterwards ( excluding weaponry of course).
How's the groupware situation on Linux? Mail, calendars, adding shared meeting rooms, etc.
Anymore I just keep Outlook web open in a web browser though. Not because Evolution is lacking, I just didn't really see the point in setting it up anymore.
KMail was actually financed for some time by the german gouvernment.
Then there's MS teams. I'd rather it just not run anywhere (die) instead of being a "good enough" solution bundled in to the suite. At least if it weren't there we could use something usable like slack instead.