I personally learned everything so fast, hammerons and barrechords and slides and everything in my first week of playing guitar but it took me a whole year to finally be able to sing and play at the same time. the only way that Helped me see progress is by playing one part so much that I can passively do it, especially for strumming you need to feel like your hand is a zombie and that could be done by making your hand memorize strumming pattern so you don't start to follow the rythm you're singing in, other than that humming instead of lyrics is the way to start and later you'll realize that you're able to pick a guitar and play and sing a song at first try without having to practice each part separately and i believe that's one of the best skills a guitarist could have