Is it permissible to collect donations to cover the mosque's expenses after the sermon and before the establishment of the prayer, given the community's financial difficulties and the mosque's occasional reliance on the bank to pay its bills, and is this act considered "idle talk"?

Fundraising should not be done after the sermon and before the prayer for several reasons: First, because the continuity between the sermon and the prayer is a condition for the validity of the sermon according to many jurists. Second, it causes hardship for the worshippers, especially in large mosques, and may lead to some of them missing the prayer. Fundraising can be done after the prayer is over, as the worshippers are leaving, unless it is impossible to do so and the continuation of the mosque depends on it, in which case there is no objection to fundraising at that time, provided the interval is not prolonged.