Azure (and AWS) offer Gov clouds, and probably on prem air-gapped deployment of their full stack of Fabric for that type of NEED security customers who can pay for it.

It is trade-off between risk and access/productivity with a cost dimension always.

Depending on your threat model you could go to typewriters /paper as some Russian department did famously few years back too.

Indeed.

If you want deniability no one should be doing business with you.