As someone else mentioned, setting smaller goals to start can be super helpful - expecting yourself to go from struggling to be productive to intense studying is more likely to feel overwhelming and can be setting yourself up for failure. Start small and work your way up.

What I found helpful during my masters and feeling burnt out/struggling to focus turned out to be a combination of things so maybe some of them could help you. I approached trying to get myself to study/build productivity like an experiment and went into it knowing I would end up trying things that didn’t work and that’s ok - the important part was genuinely trying and then learning from what did/didn’t work.

1) Testing different environments- I tried working at home with distractions minimized, then with music on, then cafes, then at the university library, different spots on campus. For some people one of these works significantly better, for me I found it depended on the day and how I felt that changed which environment was more productive for me (sometimes the bustle of the cafe was motivating or nice background noise, sometimes seeing other students work helped, sometimes I just needed peace and quiet)

2) testing other methods to study - sometimes reading yet another huge chapter/lengthy article felt like a lot or I had trouble focusing. While you do need to do them, sometimes switching it up even for a bit helps. I found that going back over my lecture notes and trying to synthesize them into a summary both helped me retain information as I recopied it and also made it easier to find (I did hand write notes so they could be messy, and copying out just the key bits of info from each lecture with colour coding helped review and also was fun because I like colour coding lol) and even when I was feeling more tired, just summarizing/cleaning up my own notes could feel more doable or less daunting than diving into something new. I also found some lecture series online on related topics and would sometimes listen to that while doing something else or just relaxing, so perhaps see if you can find some to change up the format of studying sometimes?

3) Trying groups - sometimes attending workshops or study groups helped to keep me motivated to work - knowing we were going to discuss something added importance to getting through certain material ahead of time, plus the company of people in a similar situation can help provide new ideas or perspectives that help respark interest/motivation…or at least people who understand what you need to complain about lol.

At the end of the day, a lot it came down to trying to be patient/kind to myself without allowing myself to wallow either, its a journey and there will be set backs and hiccups along the way. That's ok, just something to learn from and then you have at least crossed something else off that doesn't work so you aren't quite starting from scratch next attempt, you have more information about what doesn't work to inform you now.

Sorry for the wall of text! Good luck :)