To create a new account group, follow these steps:
Go to 'Settings' > 'Personalization' > 'Account List' > Select 'Account Groups' > Tap on the + button at the bottom right

Alternatively, you can create a new account group directly from the account list:
Go to 'Accounts' > Select an account and hold it > Tap on the + button at the bottom right

Now you have the opportunity to enter a name for your group and add accounts to the group.

Accounts, whose symbols in the selection already have a small folder icon, are already part of a group. If they are assigned to a new group, they will be removed from the previous group.