The way I learned Spring was basically by just being pushed into a Java project that was using it right after I finished uni. Tbh it was a bit overwhelming but I was able to slowly wrap my head around it in about a month or two. It was also the first “real” framework I ever used. Ever since then I started to just jump right into projects and try to grasp the basic concepts of the frameworks used, since they are mostly quite similar and try to expand my knowledge from there on. At least for me this worked well for NestJS, Flask, Django and somehow also for stuff like angular and Android development but there I had to put up with some formerly unknown concepts.