As stated in the error:
Cannot allocate memory
Magento requires a minimum of 2GB to run without these types of errors. Assuming your server has 2GB available, you still need to update the .htaccess file in the Magento root directory.
In this tutorial (How to install Magento 2.3 and build a web server), look for the bit labelled “Update memory_limit” to utilise the available memory on the server.