At the moment, only a subset of users have the ability to create or edit recurring events from within Outlook Mobile. It is a technical limitation that we are aggressively building workarounds for. It is a planned feature for everyone and we hope to bring this to you as soon as humanly possible.
If you know you have a REST account, on Microsoft 365, this feature should work for you.
In the meantime, calendar services like Google provide many customizable options for events. For example, Google allows you to customize recurring events by duration, number of occurrences, days of the week, etc. Any events created externally (in Google Calendar itself, for example) will sync properly to your Outlook calendar once it's been synced.