Which ones? Signal? Likely. Secure mail and VPN? For sure. Can "foreign agents" use them? Certainly.
Who will have a hard time to use them? General population. Signal is the privacy communication service with the lowest barrier to entry, in terms of cost and setup complexity. Not a tool for spies, but for average Joe.
What service do you recommend BTW? That ensures government cannot snoop and prevents "foreign agents". It seems that any privacy is a risk, so I'm curious what a privacy minded person thinks should be OK.