Is inviting colleagues to eat at the office, in reciprocation for a previous invitation from them, considered a bribe if the manager is present? And is it permissible to eat what they offer of food?

It is not permissible to seek closeness to a manager or official through gifts, as this constitutes bribery and embezzlement. The Prophet, peace and blessings be upon him, cursed both the briber and the recipient of the bribe. Therefore, if bringing food to the manager by colleagues aims at currying favor with him and influencing him to obtain privileges, then it is not permissible to do so. However, if the intention is to exchange kindness without any ill motive, then there is no harm in eating with them, and it is commendable to reciprocate their gesture. As for the questioner, there is no harm for him in eating from this food under any circumstance, because the reason for thehibition on the manager is not present in his case.