I'm also fairly new to TT-RSS and was a former gReader user, so I was in looking at this myself just recently.
I think at some point they removed support for TT-RSS and moved it to their new paid app, News+.
I wasn't interested in buying another app from them, so I downloaded official TT-RSS app
and also have been playing with the unofficial TTRSS-Reader
. Haven't decided which one I like best yet, but I went ahead and bought the official one anyway as a tiny gesture of support.