I was helping someone debug a recent problem with invisible virtual serial ports on a TS-890S. After a lot of head scratching, found this on

Caution!
Please do not use the virtual COM port driver v11.4.0 released by Silicon Laboratories on July 29, 2024. A problem has been confirmed where the corresponding COM port becomes invisible in our PC applications. This problem does not occur with v11.3.0, which can be downloaded from the link above. If you encounter this problem with v11.4.0 downloaded from the Silicon Laboratories website, you can avoid it by reverting to v11.3.0. (As of August 1, 2024)