Last season, several roster rules including the practice squad and Injured Reserve designations were modified and made more flexible because of COVID-19.
It appears that those rules will remain in place for this season as well.
This means that:
Injured Reserve: Teams can designate a player to the IR and have the option to bring him back to the active roster after 3 weeks. There will be no limitations on how many players that can return from IR.
Practice Squad: The practice squad will continue to be comprised of 16 players (in 2019, the practice squad was 10 players). Teams can also carry six players with more than two accrued seasons on its practice squad. Teams can elevate players from the PS to the game day roster to supplement its active roster.
I think everyone (GM's, coaches, and players) liked the modified rules last season. So it is not that surprising that these rules were carried over from last year.
https://www.espn.com/nfl/story/_/id/...ter-rules-2021