Let me share my two cents how I've solved this problem.

The issue is that new snap versions of opera lack libqxcb.so/libqwayland*.so/others qt plugins in snap container. These plugins are installed in main OS at /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/ path but they are inaccessible from recent opera snaps for some reason. Older snaps do not have any problems with them.

Quick-and-dirty fix I use (for xcb variant):

mkdir ~/snap/opera/qt5-hack/platforms/
cp /usr/lib/x86_64-linux-gnu/qt5/plugins/platforms/libqxcb.so ~/snap/opera/qt5-hack/platforms/
QT_PLUGIN_PATH=/home/user/snap/opera/qt5-hack  opera

And voila! - opera works again.

Proposed better solution: either ship these plugins in snap or connect to kf5_core snap.