All ICUs in Switzerland are occupied as of now

It's the normal capacity ICUs that are full (they use some weasel word, "pretty much full" or some such). Since the pandemic started, hospitals added more capacity. This additional capacity, together with cancellation of procedures that can't be postponed, allowed to still have some capacity left. However the standard of care is expected to be lower. Additionally, it is sometimes necessary to move patients to a different hospital, so they are asking for understanding.

Last, there is some weird language towards the end, asking at-risk people to clarify whether they "don't need life-extending care". I assume they want to know whom they should ignore?

The official numbers we get from the newspapers/state media point to 80% occupation.

https://icumonitoring.ch/

Raw data visualized: https://www.thelocal.ch/20201106/maps-switzerlands-intensive...

TLDR: not an as dramatic situation as the twitter thread proclaims. But still really serious.