Opera uses the Chromium PDF viewer extension, which uses pdfium. There's a group at https://groups.google.com/g/pdfium for discussion and a group for bugs at https://groups.google.com/g/pdfium-bugs. There's also https://bugs.chromium.org/p/pdfium/issues/list where one could file an enhancement bug.
If you get this supported in pdfium, it should then automatically work in Opera.