I use Debian, and never followed their account there. Like most "official" accounts that now make a big point of leaving X, they only posted a feed of their official pages and contribute nothing that would make it wortwhile to follow or interact with, anyway.
An explicit announcement like this, on the official news channel, is almost the definition of virtue signalling. If they don’t want to post to X, that’s fine, and an announcement on X would even be appropriate, and they could criticize X there, which would be useful information for other people using X. But a widely publicized post like this, to everybody not using X? It is obviously only done to signal virtue.
In reality, it serves an important social function. Expressing ethical values signals to others that these values matter and encourages collective action. When enough people make similar choices, it can create economic and social pressure for change. Publicly aligning one's actions with one's principles isn't just about image. It's about fostering accountability, strengthening community values, and inspiring others to reflect on their own choices.
In this way, "virtue signaling" can be a catalyst for meaningful social and economic reform.