Yes, merchants can uninstall them from Shopify settings.

Through Settings > Sales Channels > Shopify App Store > Install.

Some sales channels are installed as apps but appear as sales channels in Shopify Admin.

Yes, many sales channels are developed by third-party partners.

An app that connects Shopify products to external selling platforms.

Yes, Shopify offers a Sell on WordPress sales channel option.

A sales channel that allows products to be embedded on external websites.