How many bridge groups are supported on a firewall that operate in transparent mode?

answer is correct:

“If you do not want the overhead of security contexts, or want to maximize your use of security contexts,
you can group interfaces together in a bridge group, and then configure multiple bridge groups, one for
each network”

https://www.cisco.com/c/en/us/td/docs/security/asa/asa90/configuration/guide/asa_90_cli_config/interface_complete_transparent.pdf