Some of the subreddits in general are great, there's a few high quality Instagram accounts too if you want more gym based stuff.
r/advancedrunning and r/running are filled with fantastic information for runners.
Login • Instagram is one of the best gym type Instagram accounts I've seen, gives away a massive amount of free information including workouts and diet stuff, and has a pretty balanced approach for someone coming from a CrossFit background. Login • Instagram is another good one, he does marketing very well but his approach to strength-work fits neatly in to most training programs without having to pay for the program itself, you can piece together most of the stuff he does from his social media posts. Also has done work with Marcus Filly so you see a bit of the approaches blend together.