

I wouldn’t trust any third party claims for something as sensitive as this. You’re giving them a lot of access and trust and that’s not great for something that will directly talk with the iCloud where your passwords are stored.
Your best bet is to export those passwords to another password wallet that you trust that works in Linux.
You can access the iCloud through iCloud.com and I believe you can access passwords there, but of course it doesn’t offer the same convenience that it does on Apple devices.
I have some buds that do this and you have the ability to download languages for offline use and those work just fine.
Apple could do the same. They may not, but this is one of those features that needs offline use more than others. Some remote village where no cell towers exist, underground where no cell towers or satellite can penetrate and no WiFi exists, indoors where cell towers are difficult to penetrate and WiFi is not always an option…
Hopefully they will.