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Fairphone 5 launch event
(www.youtube.com)
This is a most excellent place for technology news and articles.
https://arstechnica.com/gadgets/2023/08/fairphone-5-sets-a-new-standard-with-8-10-years-of-android-support/
It's moot anyway, 2028 is the timeline referenced in this article citing FairPhone.
The Qualcomm product brief is copyright 2021. https://www.qualcomm.com/content/dam/qcomm-martech/dm-assets/documents/qcs-qcm6490-soc-product-brief_87-28733-1-b.pdf
Copyright may have been opposed on this document early during development. But anyway, in both case end of support is 2028, which is better than the usual 2-3 years of support for mainline chips.