It seems that starting after 10pm EST on May 23, 2023, the UPS rates stopped working for us as well.
To address this problem, we have temporarily switched to using our FedEx account for shipping rates until we can find a resolution for the UPS integration. This workaround has been working for us in the meantime.
I've read that switching the "UPS Type" to "United Parcel Service XML" dropdown option has been working for some. Stores > Configuration > Sales > Delivery Methods.
We had to do a combination of switching to UPS XML as well as "Revalidate Your Access Key". In UPS account https://www.ups.com/upsdeveloperkit > Manage Access Keys > Revalidate Your Access Key