Avalanches can start with a single stone.

EU together with UK and Canada hold more Treasurys than the entire rest of the world combined, and if they dumped them all at once it would be significantly painful for the average American as interest rates would spike, as would inflation. The Dollar would decline against most other major currencies.

However dumping that much debt all at once would require the sellers to heavily discount a large portion of their bonds, earning them increasingly fewer, and paying in (depreciating) dollars.

It's exceedingly likely that de-dollarization accelerates from here, but it's also unlikely that even the Norwegian government sells it all at once. Rather than mass selling, expect EU entities to curtail or even cease buying US bonds altogether if the geopolitical situation doesn't improve.