Same here... S20 Ultra, Sprint/T-mobile 12GB/128GB. Tried 3 different cables and hubs, even my Anker Powerport with PD. Sometimes it will fast charge, most of the time I have to keep unplugging and plugging to see if it catches. Another thing I noticed is that it will say it's fast charging and XXX amount of time until full, but the percentage never goes up even after 30 minutes of charging. Usually I'll see the "check your connection" because it will be an ungodly amount of times to fully charge the phone. So yeah, I'm pretty frustrated with this because before the update, charging was not an issue. Samsung needs to hurry up and fix this, or allow me to downgrade the firmware/software.
sometimes it evens goes down whilst charging and using the phone
i think they did something to prevent the phone from overheating but thats still happening
it really is super annoying as it seems they're trying to fix things by disabling and limiting other functionality
wish i'd never bought this phone - honestly