That would be expected then, unfortunately. This seems to be a technical limitation with those browsers, as they do not support Custom Tabs which is generally considered common practice nowadays.
See these sources for reasoning as to why this is:
While this is not a new issue with the mobile beta (it applies to tablets as well), we appreciate the feedback! This is not something that we can easily fix without workarounds that do not follow recommendations and/or best practices, so we hope that temporarily switching your default browser works for you! After all, once you have signed in you should not have to do it again.
That said, we’ll monitor the situation and if a better solution is found, we’ll of course consider improving this!
Apologies for the inconvenience in the meantime!
Kind Regards,
Malte