This is precisely why Microsoft freaked out when Germany last tried this. It led to them inventing this nebulous "TCO" concept wherein they massively overestimated the costs surrounding moving to FOSS in order to try and convince clueless managerial stakeholders to stick with them.
To be fair in certain cases the cost might be very high and considerably higher than whatever the license/subscription fees paid to MS are. e.g. Libre Office doesn’t really have a drop-in replacement for Excel (for non trivial use cases. To be fair it still might be sufficient for the majority of users, but that would mean that some proportion of your workforce has to stay on Excel/Office which kind of beats the whole purpose).
To be equally fair, in certain cases the non-licensing costs of Microsoft software are higher than the FOSS equivalent.
In fact, I'd argue that in some cases these are higher. A good example of this is that piece of shit that is Microsoft Teams - both the horrid security flaws and the ways it keeps breaking. I've used FOSS equivalents and they have a smaller attack surface and are more reliable.
They also play all sorts of user-hostile tricks that make vendor lock in possible, and this often has an underappreciated impact on delivery.
Uh using an out of date and unsupported Excel version is a really bad idea. Lots of security vulnerabilities around VB scripting/macros which gives you the very real risk of being compromised by a malicious spreadsheet.
Better to just switch where you can and invest resources into improving FOSS offerings to handle the use cases it currently can’t.
Medical researchers in many places leak non-anonymized sensitive patient data to MS, even when they know better and that's one of the reasons Office LTSC exists
The network effect may be mostly considered in regard to social media, but it is just as powerful when it come to tools and file format.
Administrations moving en-mass to open-sourced software would ensure a significant chunk of companies would follow.