Currently, the snap version of Bitwarden uses core18, presumably because that is the default in electron-builder.
It would be nice if the snap was updated to core22 due to potential security benefits and practical reasons (core18 is a rather old dependency that not many apps use and not have installed, while core22 is very likely to be installed by default).
Based on this github comment, the reason core18 is used is because electron-builder did not expose an option to choose a core version. However, based on the first bullet of this electron-builder page, it is possible to do so.