GA4 doesn’t (currently) allow you to create custom channel groupings but does come with a larger set of standard options.
To make sure your traffic lands in the correct group use this handy UTM Builder tool which also provides a breakdown of the rules Google Analytics 4 uses to categorise traffic.
These are the rules defined by GA4:
*This is the standard usage of these fields. In reality you could enter any value you want that will assist you in identifying your traffic or nothing at all.