Assets\_Project\02_Scripts\DialogueManagerBhv.cs(60,27): error CS1061: 'TextMeshProTypewriterEffect' does not contain a definition for 'onBegin' and no accessible extension method 'onBegin' accepting a first argument of type 'TextMeshProTypewriterEffect' could be found (are you missing a using directive or an assembly reference?)
Exactly. When you tick the Welcome Window's TMP_PRESENT checkbox, it can only add the TMP_PRESENT scripting define symbol for platforms that are currently installed. If you install modules for other platforms (e.g., iOS) after that, you'll have to add the symbol manually or re-tick the TMP_PRESENT checkbox.