keyword = request.form.get('keyword') search ="%{}%".format(keyword) posts = Create.query.filter(Create.title.like(search)).all()
users_created = Create.query.filter_by(author = session['username']).all()
См. http://www.leeladharan.com/sqlalchemy-query-with-or-and-like-common-filters
Вы можете связать вызовы на filter следующим образом:
filter
posts = Create.query.filter(Create.title.like(search)).filter_by(author = session['username']).all()