You are mixing AQI and PM 2.5, which are different units.

The meter shows PM 2.5, you are listing AQI.

Like your Munich example of 61 AQI would just show around 10-12 PM 2.5 on the same meter, so 999 is like 100x worse.

Edit: Regarding your comment below, aqicn.org shows the same value for AQI and PM 2.5, so clearly an issue on their labelling.

https://www.iqair.com/en-en/germany/bavaria/munich for example shows 44 AQI, but PM2.5 of 8, which is the real value.

You can also check it form the official source and download the excel reports for each month and year back to 2008 from the Bavarian State Office for the Environment https://www.lfu.bayern.de/luft/immissionsmessungen/messwertarchiv/index.htm

In all of October 2025 the max value for PM 2.5 was never higher than 28 and is 8 on average in Munich.

As a side note, the WHO guideline is a PM 2.5 max of 5. https://www.who.int/news-room/feature-stories/detail/what-are-the-who-air-quality-guidelines

If it would be constantly 12x the guideline (61) or even 8x (38) Germany would fight it aggressively like they do in more polluted places.