Do the congregants return with the Imam to bowing after straightening up from it if the Imam made a mistake and did not say: "Subhan Rabbi Al-Atheem" during the bowing, then remembered while straightening up and returned to bowing?

If the Imam forgets to say "Subhanallah" (Glory be to Allah) in bowing (ruku'), and only remembers it while straightening up from bowing (i'tidal), he should not return to the bowing position, as its time has passed. If he returns intentionally, his prayer is invalidated. If he returns due to ignorance or forgetfulness, his prayer is valid, and he should perform the prostration of forgetfulness (sujud as-sahw).

As for the congregants (ma'mumin), they should say "Subhanallah" (in their bowing) and not follow him (if he returns to bowing after rising). Whoever follows him intentionally and knowing the Imam's error, their prayer is invalidated. If it was due to ignorance or forgetfulness, their prayer is valid.