1) IRCC aims to receive up to 40,000 complete applications in 2021—10,000 from the 2020 intake process and 30,000 from 2021.IRCC invites more people to apply than the number of applications we aim to receive because not all sponsors who are invited to apply submit an application.
2) This is going to be a new pool but the people who already submited.
If you were able to submit your interest to sponsor form in 2020
If you were able to submit the interest to sponsor form in 2020, you saw a page with a confirmation number. We asked you to write down this number so you can use it later.
We also sent you
an email with the confirmation number to let you know we got your form. Once we send out invitations, you can use it to check
if you’ve been invited to apply to the 2021 program.
3) Date will be announced soon for new applicants. Invitations to apply will be sent over the course of 2 weeks, starting the week of September 20, 2021.
Source
https://www.canada.ca/en/immigration-refugees-citizenship/services/immigrate-canada/family-sponsorship/sponsor-parents-grandparents/tell-us-you-want-sponsor-parent-grandparent.html