Since there is no blog-post about the end of the project on the FAIRsFAIR website, I don't think we need to add one on our side.
But we should add in the "Hall of fame" part of this page the FAIRsFAIR project:
https://www.softwareheritage.org/support/partners/

With the link to the blog post:
https://www.softwareheritage.org/2020/12/15/fair-principles-for-software/

You can use the text from the task description:
Software Heritage has participated in the FAIRsFAIR's Task 2.4, "as stipulated in the FAIRsFAIR project proposal, is tasked with “extending the FAIR concept currently applied to data to the range of data services needed to enable and support FAIR data, and to software”. This ambition naturally splits into two related but distinct topics, namely (i) ‘FAIRness of services’ and (ii) ‘FAIR principles for (research) software’. Task2.4 will be working on these topics alongside each other, seeking synergies where possible but also mindful of intrinsic differences that warrant a parallel approach."