Bug in RDS Web Client - Copied text in RD session improperly encoded

Your byte dump is consistent with text bytes being exposed under the wrong clipboard format: CF_UNICODETEXT denotes Unicode text, and Windows Unicode functions use UTF-16. However, “Given” alone cannot establish UTF-8 specifically, because its characters have identical ASCII and UTF-8 bytes. Including an accented character and a supplementary Unicode character would distinguish those possibilities.

Since you reproduced this across three browsers and the native client behaves correctly, repeating browser reinstalls would add little evidence. Capture a good and bad copy of the same synthetic string, including all advertised clipboard formats, timestamps and client/server builds.

The RDS web client has support capture: open the ellipsis menu, choose About, start recording under Capture support information, reproduce the corruption, then stop recording to download RD Console Logs.txt. Submit that with your reproduction through Microsoft's support channel. I cannot confirm a published fix for these versions; retain the working native-client workaround meanwhile.