From Ebay's website:
What you need to know
As a UK resident, when you sell over €2000 or surpass 30 sales transactions within a calendar year, eBay is obliged to report certain personal or business information to HMRC in accordance with the UK digital sales reporting legislation. Starting January 2025, the prior year's information will be annually reported to HMRC each January and a copy of the reported data will be provided to you. When prompted to do so, please provide eBay the requested tax identification information specific to you as a business or individual. UK digital sales reporting requirements do not change your existing tax obligations or create new tax obligations for you. To find out about your tax obligations, please reach out to HMRC or a tax advisor.
I suspect the frequency of sales data reporting will vary across platforms, but that seems to be what Ebay are doing.
Good find.