OK, so the 25.0.8 ISO is unbootable for your system and as soon as you update from 25.0.7 to the 25.0.8 you get your system also unbootable.
Now we have to figure out what the regression might be.
First provide the output of inxi -zv8c0 so we know with which hardware we are dealing with.
You can try to use the 25.1.x series of Mesa via this repo. Simply place it on top of [extra] in your /etc/pacman.conf file and use sudo pacman -Syuu to downgrade.
[mesa-251]
SigLevel = PackageRequired
Server = https://download.manjaro.org/pkgs/mesa
You can also reinstall 25.0.7 add the mesa repo and upgrade to see if that change makes your system bootable again. If you already have 25.0.8 update applied you can go to the bootloader by pressing ESC key and select the bootloader entry. Press CTRL+E for edit and search for the words quiet and splash. Delete those and add 3 to the line. Then execute CTRL+x to start your session. You will land in a text console TTY. Login with your user.
Edit the /etc/pacman.conf with nano: sudo nano /etc/pacman.conf. Perform the downgrade and reboot.