Infy.uk and 000.pe was formerly available as an option for free subdomains in the client area, but now it isn’t anymore since prior issues with registries for these two domains take down the domain entirely after an abuse report.
https://forum.infinityfree.com/t/all-infy-uk-subdomains-down-suspended-by-registry/115543
But the existing subdomains under infy.uk (and 000.pe) are still active because people keep using them, even after admin advising those people to move to other available subdomains. So in theory, you can find infy.uk still there as an option in Control Panel > Subdomains 