PARADOX require ext-fileinfo * -> it is missing from your system. Install or enable PHP's fileinfo extension
This seems to be the first problem. You need to install and/or enable the PHP fileinfo extension.
If you managed to install Flarum on the same host previously, maybe it means you changed the PHP version for the command line (the same error should have prevented installation in the first place)? The PHP extension needs to be enabled for this particular PHP version (7.3 CLI)
While making sure the PHP extensions are enabled, you should also make sure you are using the same PHP version for the command line (CLI) and the webserver, as sometimes 2 different PHP versions are used. If you are on a managed hosting there's usually one global setting for the command line and one setting per host for the webserver.
The log file also seems to indicate file permission errors that prevent Flarum from writing into the <flarum>/storage
directory.