Same boat here with almost same identical timeline
Approved May 27th
Case was sent to NVC June 3rd
Still no welcome letter, only one small difference we paper filed so we thought maybe that's why our case was taking longer as USCIS still uses physical mail on some cases sent to NVC
We contacted NVC and this was their reply
"Although the Form I-797 approval notice mentions a delay of up to 30 days for cases to be delivered to NVC from USCIS, current shipping times may be longer. If you have not received a communication from NVC about this case within 60 days from the I-797 approval notice, please contact us again."