You’d need to first establish if you are an (1) independent/self-employed/business owner (on your own), or (2) employee, be it part-time or full-time. Please check the contract, and also who does the taxes and social insurances?
And in any case, since you’ve worked for two months, the company who hired you owe you the pay for these two months. That is separate from the two months you were “asked to stay at home.”
If you are (1) independent business owner, meaning, working on a complete freelance basis, doing your taxes on your own, and did not get any work hours from that employer for two months, yes, that was a decline in your revenues, and you can file for that “sustainability grant” of max. 1 million yen (or your actual loss/reduction compared with last year, whichever is lower), “IF” there was any month in 2020 where your revenues were lower by 50% or more compared to the same month of 2019.
What they are saying about “maximum” of 1 million is that for example, assuming your pay was 120,000 per month (1,440,000 annual), and if your revenue for the month of June 2020 was 50,000 due to reduced hours, for example, and it compared against 120,000 yen in June 2019, yes, you are eligible, and
S = 1,440,000 – 50,000 x 12
S = 840,000
This is lower than 1 million, so you get 840,000.
If your revenue for the month of June was 0, and it was 120,000 in June 2019, you are eligible, but
S = 1,440,000 – 0 x 12
S = 1,440,000
But this is higher than 1 million, so you get 1 million (that is the max).
All they are saying that you don’t get more than your “actual/assumed actual” loss. (Of course the calculation is simplified – by selecting only one month - to make it easy for people to apply. Your real loss at the end of the year may be higher or lower in the end.)
You’d need to attach images of your copy of “kakutei shinkoku sho” (tax filing document) from 2019, and your monthly revenue calculation for this year.
If you are an “employee” and were told by the employer to stay at home for the two months, yes, you should be eligible for the 60% pay.
But if the contract does not state any regular number of work days, you might not be eligible for that…