Blinking cursor during boot after latest update, I temporarily fixed it

There are a few potential things to look at. First, the Arch wiki page:

https://wiki.archlinux.org/index.php/NVIDIA

Second, the nvidia-installer package (or nvidia-installer-dkms) should be able to install and configure the correct driver for you.

Third, nvidia-340xx is an AUR package so might end up breaking when repo packages are updated. You might need to to wait until the package is updated (e.g. for kernel 5.8).