Not a rules change. I don't know, which cards that patch note is refering to, but both the CR rules themselves, and the reminder text for all improvise cards (including new prints, like Inspiring Statuary) spell out, that mana abilities are activated before costs, including improvise, are paid.

601.2g If the total cost includes a mana payment, the player then has a chance to activate mana
abilities (see rule 605, “Mana Abilities”). Mana abilities must be activated before costs are paid.

Improvise reminder text:
(Your artifacts can help cast those spells. Each artifact you tap after you're done activating mana abilities pays for 1.)

Is this a recent rule change, or was it wrong for this to work in the past? I see a 2024.36 patchnote that says, "Autotap now understands that some artifacts can both be tapped for Improvise and then sacrificed for mana."

The game does not allow it, because the rules do not allow it. You tap artifacts for improvide when you pay the cost, but you have to activate mana abilities to produce mana before you start paying costs. You canot activate mana abilities during the process of paying costs.