Installing Drupal

I am getting InvalidArgumentException error. 

I do not know the reason of this error. 

When a new node is created, the new node does not gets displayed due to the error. 

Tested with Drupal 9.1.5 and latest 9.1.6 and both the Drupal versions gave the same error in admin\reports\dblog

The modules uninstalled: 

How can I install Drupal on my existing Website? I want Drupal to use my font and to look like my Website like it's integrated into my Website. I am beginner with Drupal, and can you please simplify your answer?

Hello all,

Error: Call to undefined function variable_realm_get() in oa_site_layout_init() (line 64 of /var/www/html/openatrium/profiles/openatrium/modules/apps/oa_site_layout/oa_site_layout.module)

during the installation this error is appearing, I have no idea how to solve it, could you help me?

I received the following error installing Drupal 9.1.6 - at (seemingly) the end of the web-based installation:

Hi, I tried to install the template Progressive from Envato Market for Drupal 9. ( https://themeforest.net/item/progressive-multipurpose-responsive-drupal-... )

I followed all the steps, update php to 7.4, mariadb and apache to latest. I enabled all the modules and configurations to make run Drupal 9 (can do a fresh install of it without problems).