I agree with you about YAML's treatment of tabs. I still use YAML because there's often no other choice.

Python is actually flexible in its acceptance of both spaces and tabs for indentation.

Maybe you were thinking of Nim or Zig? Nim apparently supports an unsightly "magic" line for this (`#? replace(sub = "\t", by = " ")`), and Zig now appears to tolerate tabs as long as you don't use `zig fmt`. I haven't used either yet because of the prejudice against tabs, but Zig is starting to look more palatable.