You can check the mailing list and specific freezing strategy for details.
Debian 11 Bullseye releases freeze policy, adds hard freeze milestone
The Debian development team has released a tentative package freeze date plan for the next major release, Debian 11 Bullseye. According to the introduction, this time introduces a new milestone between Soft Freeze and Full Freeze, this is Hard Freeze. During hard freezes, critical packages and packages without automated testing are prohibited from migrating automatically. These packages will need to be manually lifted from the release team for migration, just like a complete freeze.
It can be seen from the timetable that the first milestone of Debian 11 Bullseye, “Transition and (build-)essentials freeze”, will take place on January 12, 2021; the second milestone, “Soft freeze”, will be added on February 12, The third milestone “Hard Freeze” is on March 12, while the fourth milestone “Full Freeze” has not yet been set.