Wireless charging is a notoriously finicky technology, with different standards and implementations for faster speeds that aren't compatible with each other. However, there appears to be a growing number of people experiencing problems with fast Qi charging on Samsung phones, even with docks that worked perfectly before a few months ago.
Over the past two months, there have been a growing number of reports about wireless charging problems on the Galaxy S20 and Note20 series. Some complaints on Samsung's support forums go back even farther, but most of the issues back then seem related to charger defects or user error. Reports rose exponentially during late September and early October, allegedly due to a system update — likely the September or October security patch.
The story is similar across all reports: Qi pads that previously charged the phone at fast speeds (indicated by "Fast wireless charging" on the lock screen) now only charge at the standard 5W speed. The same chargers still work with older phones, according to various reports. Most of the complaints come from owners of Galaxy S20 phones, including the Plus and Ultra models, but there are also some reports from the Note20/Note20 Ultra.
Samsung hasn't responded to the complaints thus far, except with generic troubleshooting steps. There is one comment from a few days ago saying another software update fixed the problem on the Note20 Ultra. Samsung began rolling out the November security patch at the end of October, so if that update contains a fix, it should roll out to everyone soon.