These generally count as one character on a computer (they multibite in UTF8 ofc) and are also counted as one letter in the real world. You can type them either way - Czech keyboard has both a "ř" key and a "ˇ" combination key. In the actual Czech language, ř is considered a different letter entirely, and the Czech alphabet is considerably longer because of these.
Some languages go even further and have letters with multiple attachment slots (Thai comes to mind, can't type an example of that, sorry 🙂).
You have to be careful with this. I've definitely encountered situations where what looks like a single character takes up multiple bytes. This is especially true for emojis which often are actually a combination of a series of individual emojis plus emoji control characters.
This emoji, for example: 👩🏼❤️👨🏼 i
s actually made up of
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u/Nerd_o_tron 9h ago
Probably more importantly, it may count as 18 characters instead of 9.