The lead settings have an option to require validation for converted leads. If this option is unchecked, then the Account validation rules will not be enforced when a lead is converted to an Account. This could result in missing or incorrect information on the Account records

The best Lightning component to add to the layout to display the 'New Task' custom action is Highlights panel. This component shows key information and actions for a record, such as its name, owner, and custom actions. Related record, related lists, and activities are not Lightning components that display custom actions. See [this article] for more information on Highlights panel.

Customers who are invited to Chatter groups can only interact with members of their groups. They cannot invite other members, @mention accounts, or request access to public groups