what does the bible say?
Online churches are specifically about watching the preaching, but a church is more than listening to sermons; it also includes fellowship. This is why Hebrews warns people not to avoid gathering together (Hebrews 10:24–25). Besides preaching, church is largely about the “one anothers,” where believers are to be together exhorting (Hebrews 3:13), encouraging (1 Thessalonians 5:11), worshiping together (Colossians 3:16), and loving each another (John 13:34–35; Romans 12:10). Churches also provide accountability (Hebrews 13:17). Finally, there are key ordinances (practices) which must be part of a church: Both baptism (Matthew 28:19) and communion (1 Corinthians 11:23–26) are only done properly as part of the gathered church.
So, while the preaching of the Word is a critical component to every church (1 Timothy 4:13; 2 Timothy 4:2), it is not the only component. The rest, the fellowshipping, can be done only in person. That said, it's fine to attend church online occasionally because of an infirmity or when evaluating a new church before considering a move. However, such occasions should be rare.