Hi @KJonsson,
First off: I’m not the one developing the product. I’m an indepentent user that helps other users in his free time. If you’re frustrated, don’t shoot the messenger.
Secondly, you can add companies by simply filtering for their company domain name or record ID. When you think about it, it shouldn’t be possible to add single companies to an active company list as that would cause all kinds of conflicts for the list filters. If a list filter conflicts your manual addition, what should the list filter do? Ignore or override your manual addition? That’s likely why HubSpot isn’t allowing this.
Best regards