Crommunity – A Flask app to build subreddit clones

I took Harvard's CS50 course and Crommunity is the final project I made to complete the Web track. Python and Flask were new to me and I had a lot of fun building this. BUT I feel like it could be improved in a lot of ways and that it's not really "pythonic".

I'm looking for a honest feedback on this. I have a lot of new features in mind, but the code is probably terrible and I'd like to get professional opinions before diving too deep...

Thanks!