When I tried to uninstall CComment Core 6.1.0 from a local test site of a client I got the following notices and warnings:

Notice: Undefined property: CompojoomInstaller::$installationQueue in [..]/administrator/components/com_comment/script.php on line 184



Notice: Trying to access array offset on value of type null in [..]/administrator/components/com_comment/script.php on line 184



Notice: Trying to access array offset on value of type null in [..]/administrator/components/com_comment/script.php on line 184



Warning: Invalid argument supplied for foreach() in [..]/libraries/compojoom/installer/installer.php on line 372



CComment is now removed from your system

The component was removed. The following libraries + plugins were still in the site (but I can uninstall them individually) :

• Library - compojoom - Site - Library - 5.3.1 - 2017-09-27
  
• Search - CComment - Site - Plugin - 6.1.0 - 2021-08-23
  
• K2 Plugin - CComment - Site - Plugin - 6.1.0 - 2021-08-23
  
• Content - CComment - Site - Plugin - 6.1.0 - 2021-08-23
  

I have a local Joomla 3.10.1 on PHP 7.4. Because it's a local test site, I have the PHP error reporting set to Development