How can you increase the time you are able to work productively?(I'm not talking about a job, talking about personal grind)

I feel like most of the times I can put in the work for maybe 1 hour and then my focus just plummets. My will to do it fades and my productivity becomes super low. I tried taking some breaks but somehow I feel still feel like I am done. Also switching to some other task doesn't seem to "reset" me.(maybe this is because the things I do are most of the times in the same area).

(Before anyone suggests sleep quality: I am aware of the importance of it. Even though it's not good, I am working on it)

How can I increase the time I put in for grinding? I am losing way too much time "chilling" and I want to fix this shit.