Hi @FacundoGorla ,
Could you please share a bit more about your scenario?
Do you want to create a recurrence event using Office365Outlook action?
The user @sumitmukund has faced similar issue with you, please check my response within the following thread:
https://powerusers.microsoft.com/t5/Building-Power-Apps/Outlook-Schedule-Recurring-Meeting/m-p/432227
If you want to create a recurrence appointment in two days of a week, I think the Office365Outlook.V2CalendarPostItem() function could achieve your needs. The screenshot as below:

Set the OnSelect property of the "PostEvent" button to following:
Office365Outlook.V2CalendarPostItem(
Dropdown1.Selected.id,
"TypeScript",
Now(), // Start time of the event in one occurence
DateAdd(Now(), 1, Days), // End time of the event in one occurence
{
Body: "Please learn it",
Recurrence: "Weekly",
RecurrenceEnd:DateAdd(Now(), 1, Months), // Repeat for one month
TimeZone: "Arabian Standard Time"
}
)
Note: The two days that you mentioned must be continuous (e.g. Monday and Tuesday) rather than separate days, e.g. Monday and Friday.
In addition, it is an known issue with recurrence event within Outlook -- each series of the recurrence event would have different event id. If you would like each series of the recurrence event have same event id, I afraid that there is no way to achieve your needs in PowerApps currently.
If you would like this feature to be added in PowerApps, please consider submit an idea to PowerApps Ideas Forum:
https://powerusers.microsoft.com/t5/Power-Apps-Ideas/idb-p/PowerAppsIdeas
Best regards,