To be fair, giving a company that’s been failing to get themed icons to work on Android for almost four years now less than a month to make a significant change to a core part of their software is… quite weird?
Like, the EU usually gives companies at least half a year to comply with smaller demands than this, because companies with such a huge bureaucracy load wouldn’t even be able to change an app logo in such a short amount of time.
Licensing the source as GPL doesn’t really force the copyright holder (which is 100% BitWarden due to their Contributors Agreement^*, no matter who contributed the code) to do anything - they are absolutely free to release binaries built on the same codebase as proprietary software without any mention of the GPL.
For example if I write a hello world terminal program, release its source code under GPLv3 and then build it and give the built binary to you (and a permission to use it), you cannot force me to give you the source code for that build because I never gave you a GPL licensed binary.
If you were to take my GPLv3 source code and distribute a build of it however, you would have to license your binaries under GPLv3, because that’s the terms of the license I provided the source code to you under. Your users would then have the right to request the source code of those binaries from you. And if you released the build under an incompatible license, I (but not the users) could sue you for violating my license.
License violations are usually not resolved by making the violator comply retroactively, just going forward. And it’s the copyright holder (so BitWarden themselves) who needs to force the violator to comply.
^* this is the relevant part of the CA:
It is followed by a workaround license for parts of the world where copyright cannot be given up.