I know it's privately held and can't buy stock in it.

I realise that this is the premise of the Musk takeover. How does that work in practice? Twitter was a public company, with plenty of current and former employees having shares due to compensation.

Were these people forced to accept money over their legitimately held shares? If not, is it now illegal for them to sell their shares?

In other words: I can see that it is no longer traded at the stock exchange, but I don't know enough about stock to understand how the genie is forced back into the bottle.

I owned Tiffany stock when it was taken private. I received cash for the shares.

This is definitely what happened for vested shares. You'll get whatever price Elon promised to pay. No idea on unvested.

I am not sure how it works in the US, but in the UK, an entity that buys at least 90% of a company can force the minority shareholders to sell at the same price.

There are no shares for them to sell because it is a private entity.

Their RSUs/equity would have either been deleted, converted to private equity that you can maybe sell on the secondary markets at best, or converted to cash bonuses.

I think 1/3 are pretty unlikely and 2 would have those RSUs in the gutter as well.

Maybe a disgruntled Twitter employee could comment.