payload.de offers a common endpoint for the Ethereum blockchain to send private transactions and bundles:

https://rpc.payload.de

Built blocks are submitted to the following relays:

• https://relay.flashbots.net
• https://relay.ultrasound.money
• https://agnostic-relay.net
• https://mainnet.aestus.live
• https://mainnet-relay.securerpc.com