Pre-IPO investors fund the company but it isnt like they give all the money upfront. They do it in pieces and can increase or decrease as targets are reached, failed, or pivoted. This keeps the investors less likely to lose money. As debts and losses are shown the value of the company dropped and how much money is on tap for the future decreases. In this case 72B of funding was "lost". This is paper money because they only had it on paper they didnt have the gold in hand.

Essentially their potential value to their current investors dropped 72B.

The reported net loss is real as they used more money than they made.

Neither factor is going to bankrupt or close the company considering they still have a bunch on hand and their investors still seem to think theres a possibility of profit (just less than before).

That's my non-expert understanding anyway.

It's not 72 billion dollars lost related to the business.

The money didn't exist and wasn't spent.

It's not clear what the instrument was exactly (I would need to look it up myself, not an accountant). But there are a range of charges that aren't actually related to profitability of a business. Value of instruments could be tied to a capital raise earlier. EG if they promised a percent of the company as part of a raise, and Anthropic is worth a lot more now. Their liability increases (the percent they owe is worth more now) and they book as a loss.