I got the following reply from the support team:
"
Hello, welcome to Outlook Mobile Support! My name is Cosmin and will help you!
Unfortunately, this is not a functionality in the app for now :( ! At the moment there is a work around, if you need to open a link in your browser you will need to click the link, then tap on the overflow menu at the bottom and choose "Open in Browser"
But please help us make Outlook better by suggesting it as a feature if you think that would be a nice addition.
Just go to Settings -> Help and Feedback -> Suggest a Feature. Developments are made based on the statistics generated by the users in this area, so don't forget to voice your wishes there!
Wish you a nice weekend!
"
This means the only properly working workaround is to use a different mail client...