Error 500 when trying to Upgrade from 8.4.2 to 9.0.0 / 9.0.1 / 9.0.2

[Iphahla]

Tried to upgrade to Versions 9 (all of them). I keep getting the same error 500 every time. I am not a coder and I don't have CLI (also don't know how it works).

* Update: I am also unable to download any attachments after the attempted Upgrade.
* Update: Font on 8.4.2 also now affected by the attempted upgrade. as per attached photo

After The attempted upgrade, the system automatically keeps disabling the Cache / Cron and puts me in Maintenance mode.

What are my options to rectify this? I use Sales Pack, and upgraded to version 2.6.3 without any issues.

Any assistance will be appreciated, as this is our core system at work and it needs to function 100%

[Kharg]

What extensions are installed in your instance?

did you get any other errors apart from the 500 one? Like a more specific one? Can you check/upload the latest logs from espocrm/data/logs ?