No surprises here.
It always struggles on non-web projects or on software where it really matters that correctness is first and foremost above everything, such as the dotnet runtime.
Either way, a complete disastrous start and what a mess that Copilot has caused.
I have so far only found LlMs useful as a way of researching, an alternative to web search, and doing very basic rote tasks like implementing unit tests or doing a first pass explanation of some code. Tried actually writing code and it’s not usable.
OTOH webdev is known for rapid framework/library churn, so before too long there will be a crossroads where the pre-AI training data is too old and the fresh training data is contaminated by the firehose of vibe coded slop.
And the quantity of js code available/discoverable when scrapping the web is larger by an order of magnitude than every other language.