They have. Rivian has delivered Amazon delivery vehicles which make deliveries:
https://www.youtube.com/watch?v=rJJNTVy62PU
https://www.youtube.com/watch?v=9LGtskt4YGA
https://www.youtube.com/watch?v=AzRDuLo3K6Q
Deliveries of the R1T should start in September after being delayed:
https://www.thedrive.com/news/41578/rivian-r1t-deliveries-ar...