Controllers only.
Call of Duty League 2021

The 2021 season for the Call of Duty League is making the move to the personal computer, or PC for short. The league, which was typically played on the PlayStation 4, will make its PC debut for this upcoming 2021 season.

There's just one small catch.

Even though the league will be playing on PCs in 2021, players will not be allowed to use a mouse and keyboard.

Today, the League is announcing it will move pro team competition to PC + Controller beginning with the 2021 season. This means that all pro matches will be played on PC and all pro players must use a League-approved controller of their choice.

As part of this transition, Call of Duty League competition will maintain exclusive use of controllers for the upcoming season. This change provides players with expanded choice of controller, allowing them to select the League-approved controller style that works best for their game. More details and rules pertaining to peripherals will be released at a future date.
That sure is a weird thing to mandate. Why move to PC if you are going to force everyone to stick to using controllers? Maybe we'll see the 2022 season fully transition to the PC environment, complete with mouse and keyboard usage. It is assumed that the 2021 season is sticking with controllers so that those who have practiced on controllers in anticipation of the 2021 season still being on the PlayStation 4 wouldn't be at a disadvantage.