Question: Could it be possible to have a content rule that redirects the user to another page ( similar to what c.onlogin once did), or would this be impossible 'due to how content rules work/that several rules (theoretically) might get triggered for same event)
Yes it should be possible. Events run after the main response has been made but before that has been sent back. So you should be able to modify the response I believe.
UPDATE: The above is NOT true. I think this depends on Plone version. For version 6.0.10.1 the same error occurs. That is also true with the default 'logged in message': In other words: the message Info: Welcome! You are now logged in. is not shown anymore
UPDATE: This is not true too.
The events / rules fires if the user logs in from '/login'. If the user logs in via the pop up login form, it does not. The (current) workaround is to disable/remove 'modal = {}' in portal_actions
I have a content rule for 'first login', this works (and can show a message or send an email)
I also have a redirect content rule, and this works for example if I use it for 'objects added to a container'.
But they can not be used 'together'. Any suggestion on how to troubleshoot this? Maybe there is another 'redirect that kicks in'?