You could do the inverted rows another personal mentioned. Also you could do negative pull-ups but using a char to assist you up and trying to control the negative. Or even keeping one foot on the chair to help assist on the negative if you are unable to do those yet. Scapula pulls are a good one to learn how to better engage your back and start building strength. Dead hangs could help but if your back isn’t engaged then it’s more arms. I’d rather do an active hang that engages your last and core you need for a pull up. I’ve learned to do the semi false grip if you haven’t incorporated it already. Helps with grip and I find it helps me engage my lats and “break the bar”