Let's educate ourselves now. Let's start with open source: this is a software that potentially allows everyone to see it's code and correct it if there is an issue with it.
For closed source: it is a software that hides it's code from the public. Thereby making it's users to trust them with addressing whatever issue it has in the code.
Neither of them are certain of complete security. There is still a likely hood of each or both to get hacked. So let's not shift blame to closed sources.
You’re not getting it do you?, this is not an open source VS closed source matter.
The attack was successful because someone opened genuine devices and inserted cellular implants that could read people’s seed phrases off the screen during setup and then resealing them.
The attack vector was never because of the fact that ledger was a closed source wallet or the inability for external parties to audit it’s source code, the failure was in the distribution channel and the physical integrity of specific units.
So even if it was an open source wallet and it had the same vulnerabilities, it would have still been drained through the same way too.