FWIW, Mr. Musk has a history of creating only closed, proprietary things.
He's a mix of the two really(open and closed) like all giant tech companies at this point.
Name me one large tech company that is open? Apple? Google? Microsoft? Literally all of them have some closed eco-systems and do aggressive patent enforcement.
Microsoft today is hugely open source. VSCode is open source. WSL is hugely built & expands on open source. They release their Azure networking distro open source. They would have collapsed into Cuisinart irrelevance if not for open source.
Asking whether companies have proprietary closed source is not the right question. Looking & jduging the bigger picture, of whether we- Tim Oreilly style- create more value tham we capture- is the metric. This small view you presemt that any proprieary software means open source is irrelevamt is blinders, ignores the active change underway, ehere more and more keeps getting open sourced, to remain relevant & interesting & active. Contrary 100% to your pro proprietary position, I see no companies succeeding without doing open source, without participating.
Azure is not open source, a few components are but the vast majority of it is a closed eco-system, especially compared to something like Open Stack. I was part of the Open Stack consortium that tried to get Amazon and Microsoft to adopt Open Stack or at least use open cloud standards and they refused for competition reasons. Closed cloud systems and vendor lock-in massively benefit them. Microsoft biggest money makers like their enterprise software and operating systems are all notoriously closed source and tightly guarded.
Google has been using their position to make previously open systems like Android much harder for anyone to run without their "Google Play Services" and trying to force standards onto chrome and chromium that will make ad-blocking much harder. Don't even get me started on what a disaster AMP is for an open web and how google continued to push it even when these concerns were raised.
Yes Google and Microsoft make significant contributions to open source, this is like me saying that Tesla did a good thing by opening up there patents. Big players occasionally do good things but it doesn't whitewash away the closed systems they make most of their money from.
Apple is far less political than Twitter. This move is without precedent.
That some of the public activity is political is an happenstance incident, deserving little more note than that there are super popular (by their scale) cepholopod communities on twitter.
And "the algorithm" and the moderation are incredibly tolerant, extremely accepting & broking only the few things which they legally feel they must.