It's not an OS problem but it came with new version (>=16) Markdown's js problem
Both of my MacOS and Windows 7/10 got the same problem after updating my version from 0.13 to 0.16
If post new thread, the new post's title has no issue with input any character but the 'Markdown text area' prevented the input-window to hook the text area 'Dom' and triggerred the issue. iOS and Android seemed using a different way to handle the input characters, so, this issue not showing in mobile devices.
By the way, users can type Chinese characters first anywhere else then copy-paste the content to the markdown text area, it works but not a user-friendly solution to webmasters to provide to their users.
My temporary solution is to disable the 'Markdown' extension, yap, everything goes fine. Of course currently only very plain text can be inputted.
As you might test in my website https://forum.kannz.com
looking forward to hearing the patches from markdown extension author to locate the issue and fix it, thank you for the hardworking