Upgrade from v3.0.3.2 to v3.0.3.6 Store wont load error 500

Hi,

I have just upgraded my dev store as per subject. I have gone through suggestions on forum but have had no success in getting store back online so looking for some help please. So to confirm:
1. Old version that was working v3.0.3.2
2. Updated PHP to PHP Version 7.4.13
3. Used /install/index.php?route=upgrade/upgrade to upgrade to v3.0.3.6. Reported successful
4. Opened store front end (admin & normal access) and got error 500. Removed cookies for browser and even tried a different browser. Still not working.
5. Checked config.php for define('DIR_STORAGE', '/var/www/oc_storage/'); Folder is present on my server
6. Uploaded my backup of oc_storage to /var/www/oc_storage/ Still not working.
7. Added to my .htaccess php_flag display_errors 1 but does not give me any further info on issue. Still not working.
8. Using default theme
9. Updated VQmod to vqmod-2.6.4-opencart.Still not working.

So at a bit of a loss as to what is causing this so if anyone could provide any pointers as to what else I can do it would be greatly appreciated. Thank you.

Additional Info:
Apache/2.4.29 (Ubuntu)
mysqlnd 7.4.13

Any other info required please ask.

According to what I have been reading about, OC v.3.0.3.6 is not
yet capable to handle PHP v.7.4.13, try PHP v.7.2.x or 7.3.x .

The storage folder must be inside the www folder prior to upgrade. Once the upgrade completed successfully, the storage folder must be moved back outside, both ways configured with both config.php files. As for error 500, error logs are a priority on the forum to acquire assistance.