That’s right, I don’t need to uninstall it before installing the APK. It works now, thanks.
Auto-updates were enabled, but I wasn’t excluding F-droid from battery optimizations. Maybe that’s why I didn’t get any updates notifications. But I can’t say I would have updated sooner if it was the case.
Also, if you are using any VPN or local VPN, your internet connection may not work at times when the IP changes. That is why you were getting “waiting for download”. This is the actual reason. For battery the 3rd and 4th points are valid.