There is no such functionality out of the box.
Consider to use Custom Activity to implement that functionality. The process is a bit complicated but eventually you can develop almost any functionality, since custom activity its external application that connected to Journey Builder.
Check this video for more details: Create Your Own Journey Builder ...
Salesforce support confirmed what I was thinking, it is not possible:
Hello Jeremy, how are you?
My name is Daniel from Salesforce Support Team and I took ownership of
I would like to inform you that Journey Builder does not create
Chatter posts or has any activity for this use case.
You can check all Journey Builder canvas ...
Yes, You can pre-defined the from address on an email action. Open your action, click new on pre-defined field values section.
Select from in the field to be pre-defined and then select the email address you want to default for your email action in specific value dropdown and save it.
Read more here:- Set Predefined Field Values for Quick Action Fields