Currently, Qt OPC UA does not have its documentation tied to specific versions of Qt.
But, Qt (5.12 LTS) ships a certain version of QtOpcua, which has already lots of differences to current QtOpcua documentation.
Is the QtOpcua development then done so, that it stays backwards compatible, so one can use Qt 5.12 but update the QtOpcua only, and keep up?
Which does not matter, documentation should be versioned and accessible.
Still, obviously it is just not good idea to use a library of which documentation just disappears suddenly. Documentation should be still accessible.
Maybe I'll create a mirror of https://doc.qt.io/QtOPCUA/ and version it myself.. [SOLVED]
edit: Oh, in fact my QtOpcua client code is from last year, so it is older that of 5.12... which why there is so much differences to current..