My 1 cent cotnribution to the discussion. I am still using this App by downloading it directly from the website, at their very own main webpage, without using any appstore. I’m doing this on Xperia 10 ii with SFOS 4.5.0.19, a very old LG Wine phone (foldable with physical buttons) with Android 5 and play store deactivated: it works at every update.
On the other hand I got issues with QR code pairing as second device on a brand new Samsung A33 5G, while an old Samsung S duos with Lineage OS fails to install it because Whatsapp says “please download from play store”