I've noticed none of the retailers in EU that I checked have any CSS610-8G-2S+IN in stock. When asked I got responses they had none in stock for a couple weeks to almost a month now.
A lot of other Mikrotik hardware is also either out of stock or available in very limited quantities.

I know there is a chip shortage going on, but should I expect availability in EU to improve short term? I can delay upgrades by up to several weeks, but if that changes nothing I have to start evaluating other vendors.

I got some updates from more retailers and it's not looking good: they don't expect to have any for at least 3 months..

I think you should contact sales@mikrotik.com .
https://mikrotik.com/aboutus

Try Cisco. You'll only have about 18 to 24 months to wait for them to fulfill your order.

Try Cisco. You'll only have about 18 to 24 months to wait for them to fulfill your order.

The bigger problem here would be that I'd end up with Cisco gear.

Worldwide chip shortcoming. Logistics problems (seriously, hard times due COVID).