Channel is calculated based on source and medium (but mostly medium):

ChannelSourceMedium
Direct(direct)(none)
Organic Searchgoogle, bing, yahoo etc.organic
Paid Searchgoogle, bing, yahoo etc.cpc, ppc, paid_search, retargeting
Paid Socialfacebook, instagram, linkedin, twittercpc, ppc, paid_social
Organic Socialfacebook, instagram, twitter, tiktoksocial, organic_social
Displaygoogle, doubleclick, criteo, adrolldisplay, banner
Paid Videoyoutube, hulu, vimeovideo, cpv
Affiliatesaffiliate networks, partner sitesaffiliate
Emailvaries (e.g., mailchimp, activecampaign)email
Referralvaries (referral sources)referral
UnassignedWhen none of the above criteria match

Right now, GA Connector’s calculation of channel doesn’t fully match Google Analytics standard definitions. For example, if fbclid identifier is present in the URL, the channel will be attributed to Paid Search.