Why is TestFlight review taking so long!!!

If this is the first build you submitted for external testers, it does need TestFlight App Review before they can install it. Internal testers who are App Store Connect users can usually test an eligible build without that review. Check the build status under App Store Connect > TestFlight > iOS Builds, and open App Review there if the build was rejected. Are you waiting on external testers or internal testers? Apple’s overview: https://developer.apple.com/help/app-store-connect/test-a-beta-version/testflight-overview/