Start date of ILR 12-month period prior to Naturalisation

[Grast]

Hello

I've searched the forums and have read the gov.uk guidance but seem to be unable to find specific advice on this.

Background

1. I am not married to or a partner of a British citizen
2. Tier 2 (General) Entry Clearance expired on 20 June 2020
3. Successful ILR decision letter received on, and dated 24 July 2020
4. BRP date of issue printed on the card is 24 July 2020

Question
For the purposes of fulfilling the "you should have been free from immigration time restrictions during the last 12 months of the 5 year qualifying period" requirement, what is the start date of my ILR?

Did my ILR start on:

1. 21 June 2020 (the day after my Tier 2 Entry Clearance expired), hence I can apply for naturalisation on 21 June 2021 at the earliest
2. 24 July 2020 (the date of the decision letter as well as the issue date of the BRP), hence I can apply for naturalisation on 24 July 2021 at the earliest (if this is the case, does this mean that from 21 June until 23 July 2020 I was still on Tier 2, as extended by section 3C of the immigration act, and that the ILR effectivity was not retroactive?)

[CR001]

24 July 2020 (the date of the decision letter as well as the issue date of the BRP), hence I can apply for naturalisation on 24 July 2021 at the earliest (if this is the case, does this mean that from 21 June until 23 July 2020 I was still on Tier 2, as extended by section 3C of the immigration act, and that the ILR effectivity was not retroactive?)

This one. It is the date if ilr grant/issue. Until ilr is granted, your existing tier 2 conditions continued. Ilr is never "retroactive".

Your tier 2 expiry date is irrelevant to the mandatory 12 months on ILR requirment for citizenship.

[Grast]

Thank you for the very swift response; understood.