I think at least Tier-1 ISPs that provide nothing but connectivity should be treated as utilities. They're used to engage in speech but have no business regulating it, any more than telephone companies or banks have the right to deny service based on political disagreements.
If there are ever limitations on access to basic communications, it should only be after actual criminal proceedings.
Should being the operative word. I think we both know Congress would inevitably try to use the fact those ISPs have no constitutionally protected rights (in the scenario corporations didn't have rights) to assert otherwise. IIRC 1A is what allows ISPs to operate without the US Government being able to censor via that route, since without 1A Government could regulate
what traffic ISPs are allowed to handle and could prohibit them from passing along "censored" data.
As for things like Facebook and Twitter, the government shouldn't be allowed to use those as a default way of communicating with government agencies. There are plenty of things from the federal to the local level that are now virtually impossible to access in any reasonable way without some kind of social media bullshit. And then you have incredibly problematic like Twitter deciding they get to forbid the literal fucking President from using a communications medium.
I'm not sure this one was relevant to what I was saying since it doesn't sound like a "corporate rights" issue, but that aside...
Government is more or less reliant on third parties for its communications to the people since it has no real way to communicate directly to people. The default has been via press conferences to mainstream news media/reliance on news media to report what government is doing, but social media itself is semi-replacing old news media already. So it does kind of make sense for it to eventually swap to that medium.
As for government to government, yeah that
should be only done via memorandums and such, but the Constitution didn't dictate how government communicates with itself, so it's more or less up to each branch to decide for themselves. I'm not sure Congress could even pass a law to dictate how the Executive branch communicates without tripping all over a big heaping pile of Separation of Powers, and can't tell POTUS to do fuck all.
POTUS could make pissing in the snow the official communication method he employs if he so chooses.
And then you have incredibly problematic like Twitter deciding they get to forbid the literal fucking President from using a communications medium.

They're as of now still a private company. Until/unless social media is deemed a public utility not much to do about that, and even then it's pretty damn iffy if government could force them to accept government officials as clients, at least without invoking National Security voodoo.
I'm not so much pissed with them over booting the former POTUS as I am that it was overtly politically one sided. Banning Trump while letting, say, Iran's assholes in charge openly inciting violence is a double standard that
should land them in hot fucking water just with their own terms of service.
I'm a bit surprised they haven't been sued for breech of contract, since it'd be pretty easy to convince a jury that Twitter (and other social media) are using a double standard for enforcement of their ToS, especially since they've slapped enough mainstream conservatives with money to burn on such a lawsuit.