I was not good at using Czech keyboard layout on Mac.
But here is a good document. https://www.czechclass101.com/blog/2020/10/16/how-to-type-in-czech/#3
The tip is to show keyboard viewer, and use the key "+" that is a modifier key to enter extended characters in Czech language.
- "+" + letter => long letter.
- Shift "+" + letter => ˇ + letter.
- "+" + u => ú, Shift "+" + u => ů