cannot upgrade to 9.1.1

[czv]

Hello, cannot upgrade to newest version.
espocrm@crm:~/public_html$ php command.php upgrade
Current version is 9.0.8.
EspoCRM will be upgraded to version 9.1.1 now. Enter [Y] to continue.
y
This may take a while. Do not close the terminal.
Downloading...
Upgrading...
Initialization...
Copying before upgrade files...
Rebuilding...
Before upgrade script execution...
Rebuilding...
Copying files...
Rebuilding...
Copying after upgrade files...
Rebuilding...
After upgrade script execution...
Reverting...
Unknown error on shell_exec.



in logs:
[2025-05-13 02:39:46] ERROR: (0) Uncaught Exception Error: "Class "DOMDocument" not found" at /home/espocrm/public_html/vendor/league/html-to-markdown/src/HtmlConverter.php line 113 :: /home/espocrm/public_html/vendor/league/html-to-markdown/src/HtmlCon
[2025-05-13 02:39:46] ERROR: Upgrade Error:

[lazovic]

Hi czv,

Please tell me if your instance has any modifications or customizations?

I kindly ask you to note that I have upgraded instances several times in a row from the same version of EspoCRM to the latest but have not encountered such an error.