Firestore - how to structure a feed and follow system

I was using Firebase realtime database for my test social network app in which you can just follow and receive post of people you follow. A traditional social network. I structured my database something like this-

Users
--USER_ID_1
----name
----email
--USER_ID_2
----name
----email

Posts
--POST_ID_1
----image
----userid
----date
--POST_ID_2
----image
----userid
----date

Timeline
--User_ID_1
----POST_ID_2
------date
----POST_ID_1
------date

I also have another node "Content" which just contained id of the all the user post. So, if "A" followed "B" than all the post id of B where added to A's Timeline. And if B posted something than it was also added to all of its follower's timeline.

Now this was my solution for realtime database but it clearly have some scalability issues

• if someone have 10,000 followers than a new post was added to all of the 10,000 follower's Timeline.
• If someone have large amount of posts than every new follower received all of those posts in his Timeline.

These were some of the problems.

Now, I am thinking to shift this whole thing on firestore as its been claimed "Scalable". So how should I structure my database so that problems I faced in realtime database can be eliminated in firestore.

from Firestore - how to structure a feed and follow system