I've changed permissions for folders to 775 and for files to 664 and ownership to magento user, but I'm still facing this issue.
Is to possible to happen because I've installed magento by web and now i'm trying to upgrade with composer?
Any other ideas?
I just renamed 'vendor/magento/magento2-base' folder. After that I run 'composer install'. As a result, 'magento/magento2-base' package was automatically installed and everything worked again.
Please be more specific.
The folder "vendor/magento/magento2-base" is there before updating from 2.3.3 to 2.3.4.
Did you rename it to something else?
Thanks a lot @sanuspg for the help. It saved my lot of time. After rename folder and run composer install command it's working for me. Thanks.