

WhatsApp requires that you have a mobile device (Android or iOS) connect through the official client at least once every two weeks. They also monitor for “suspicious” API usage, and will ban accounts for using their service wrong (though it is very uncommon and often temporary).
The only mostly FOSS third party solution I am aware of is the mautrix-whatsapp bridge. The developer of that bridge also created Whatsmeow, a WhatsApp Golang library.
mautrix-whatsapp requires a mobile device to connect using the official WhatsApp app. It pretends to be a WhatsApp Web client, and allows you to send and recieve WhatsApp messages on Matrix. The bridge (effectively) requires hosting your own Matrix homeserver, so it’s not a simple solution.

To add to the other commenters reply;
When Jolla does something, like make new software or patches, most of that is proprietary. They’re creating their own thing, and nobody outside Jolla can benefit from their work. That’s fine, but pretty much equivalent to any other corporate-owned mobile OS in terms of freedom, like Google’s Android.
There’s more open options, but they all have their differences. Ubuntu Touch (or really anything on UBPorts) has some components you would also find on Linux, but still uses the OEM kernel and proprietary Android device drivers. This means that devices are much more likely to work, but you rely on the OEM to maintain support for the device on Android. postmarketOS (and others, like Mobian) try to build most things from scratch instead. This means less hardware is supported, and functionality is often not great. However, all development is open, and they’re trying to ensure there’s little to no reliance on OEMs. This theoretically makes for much better (community supported) future proofing.