When am I eligible to apply for ILR? BRP Issue Date or Vignette sticker date?

I am an Indian citizen. I moved to the UK on Tier 2 (General) Visa/Skilled Worker Route.

I am looking to apply for ILR but I am struggling to determine when the qualifying period starts and the earliest I can apply.

First BRP Issue Date: 07-Sep-2020
Visa Vignette sticker on Passport valid from: 24-Nov-2020 to 22-Feb 2021
Actually entered the UK: 14-Feb-2021

There is a large gap of about 2.5 months between the BRP Issue date and the start date on the Visa Vignette sticker as this was during COVID time.

Considering the above dates, what is the earliest date that I can submit an ILR application? Is it 28 days before the BRP Issue date or 28 days before Visa Vignette date?

The qualifying period is counted from the very first date of visa approval, which for you is the first BRP issue date. The 28 day concession means you will be eligible for ILR (i.e. ILR can be granted) within 28 days of completing your 5 years.

The date of ILR application is largely irrelevant.

Read: Applicants can benefit from the date of the ILR decision

Thank you Zimba. In the Visa approval letter I received along with my passport (and Visa Vignette), below is the wording.

"Your application for a UK visa has been successful. This means that when you arrive in the UK you will have permission to be in the UK (known as Leave to Enter) as TIER 2 (GENERAL) MIGRANT
from 24 Nov 2020 to 14 Sep 2023."

My Visa Vignette also starts from 24-Nov-2020 however the "Issue Date" on my first BRP is 07-Sep-2020. Can you still conclude that the qualifying period starts from 07-Sep-2020 and not 24-Nov-2020?

I am being extra cautious as I don't want my ILR application to be rejected for applying early but I am also worried about the upcoming changes in the ILR eligibility from 5 years to 10 years as per the whitepaper released last month.

BRP issue date should be used as that is your actual visa approval date. While your visa was approved, you still needed a sticker to enter the UK and that was issued later. For administrative reasons, a visa sticker cannot be backdated so the sticker is issued from the date it is printed which means it will have a later date. However for calculating the qualifying period for the purposes of ILR, the first visa issue date is considered. Note that you are not the first person getting this advice and these are common knowledge in the immigration system