Hi, I can also recommend the udemy courses from Heath Adams. They are sometimes offered cheaply , like around 20$ . He uses htb mschines (older) ones to explain the concepts of linux priv esc and Windows priv esc. Also you csn take a look at TryHackMe which i believe is more beginner oriented.
Have been sitting in the same boat about a year ago. Extreme steep learning curve. And it can get really frustrsting at times. But just keep going and you will notice your progress after some time. Ippsecs videos are a goldmine as has been mentioned before.
Best