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.

Through my entire stint having to use it in Europe, the closest I could find was a webview for the web client: https://f-droid.org/en/packages/io.kuenzler.whatsappwebtogo/

Sadly, they enforce use of the official client to create an account and resync whenever the web client session expires. Even once got locked out for using the official client downloaded from Aurora Store, apparently I ought to have to downloaded the APK directly from their website, if not from the play store.

Edit: I also think potential legal pressure also contributes to a FOSS client not existing. Last time someone tried making a feature-complete FOSS Instagram client, they stopped after a cease and desist from Meta.

Obligatory, I would have loved to go without anything Meta in the first place, but if you've spent any time around non-techy colleagues in Europe, you'll know how much of an uphill battle it is.

Beeper works for me. Have Signal and Instagram DMs in it as well, all in one place

You could put another book's cover on mein kampf, it would still be mein kampf

Maybe read a different 'book'?