It seems fairly likely that the pandemic is largely responsible for the reported declines in average publishers and Memorial attendance.
However, with the provision to write letters and to report as little as 15 minutes preaching per month, the significant reduction in preaching hours does not seem to be entirely limited to the pandemic. The 2020 report starts from September 2019 before the pandemic, and yet the peak publishers for the year is only 12,691 higher than the peak for the previous year. For comparison, the peak difference between the 2018 and 2019 reports was 103,208.
If the pandemic is largely responsible for problems with reporting, then it would be expected to see an artificially inflated increase after the pandemic is over, accounting for any actual increase in addition to numbers recovering from potentially unreported details from 2020. This could be as much as 3% if the actual increase independent of the 'recovery' is around the 1.5% mark of recent years, which the Watch Tower Society may dishonestly hail as 'remarkable' growth.
It should also be borne in mind that the pandemic is ongoing and that the 2021 report will include data starting from September 2020. So statistics (possibly with a 'phantom' increase as described above) may not recover fully until the 2022 report.