Please check we added our Joomla Blank template for download for Joomla 4.
Download Joomla Blank template
Please download empty template for joomla 4 (without QuickStart) and install to your site.
Please backup your site before update, with that you not lost nothing important.
By the way, Are you sure the error go from OS Joomla blank template ?
we installed this template to last joomla 3.10 and your PHP version and for us all work good.
Please in joomla admin menu: System->"global configuration""->Server: "Error Reporting" - turn to "Development"
Please in joomla admin menu: System->"global configuration""-> System -> Debug Settings ->YES
and check your errors again
Regards
OrdaSoft team