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 ?

[Iphahla]

I've uninstalled all additional extensions prior to upgrade (like TCPdf).

Error 500 pops up and then when dismissed, Error message: Error: null displays on screen on top of page.

Check the error log: all I could find was Error 500: Php 8.1 ..... was invalid. I upgraded to Version 8.3.

Still no luck

* Update: Error log:
ERROR: (500) Package Archive does not exist. :: POST /Extension/action/install :: /home/iphahlac/system.iphahla.co.za/application/Espo/Core/Upgrades/Actions/Base.php(176)