You can find the mastercopies from November 2019 till August 2020 freely available in the telegram channel @enigmaias, it may come in handy for Prelims 2021. Though, this year Current Affairs questions were lesser in number, next year the trend can change. Also there were questions from Hindu articles of 2018 and before, in this year’s paper. So for Prelims 2021, current affairs content from 2019 may help.
Now considering the Prelims 2020 question paper, cutoff is expected to go down from past year , though not by a significant amount (i.e. never expect cutoff will be as low as 85 or something as some predictions say) due to two reasons. The paper was difficult, showing a change in pattern (significant reduction in Current Affairs) from previous year and the lesser number of students attending exam due to Covid-19 situation.
So if you are preparing for Prelims 2021, always aim to score well above cutoff maybe 10 or 20 marks above. Generally speaking you need to increase your attempts to 80-85 questions and reduce your wrong answers to below 25. Around 20 wrong answers with that attempt will guarantee your success. At the same time as the number of wrong answers approaches 30, your probability of success will reduce.
Another crucial factor is time management. Instead of seeing prelims as a 2 hour war, approach it as 30 minute battles. That is every 30 minute, you should cover 25 questions and mark it in OMR sheet (not all but the answers you are almost sure of, the doubtful ones can be marked later). By that strategy you will get enough time to answer 80-85 questions.
Now regarding Mastercopy Compilations for Prelims 2021, we have no plans as such to continue with the programme till Mains 2020 is over. So if you want to shift to some other good sites, you may shift.