This has already been reported by a few users, but just to add to the mix, am also experiencing this today.
Fine yesterday (well, relatively speaking - as fast as usual), but today GA4, Google Ads and even the GSC connectors are either very slow, or are timing out and returning a system error.
Very annoying.
Have tried to refresh the connector, but with no luck.
No idea if Looker Studio Team actually monitor this channel - but pinging here, just in case.