If you try to write a comment in a Handsontable cell, the comment is written in the cell itself.
However, comments depend on IME such as Japanese input.
This does not occur when using English input, such as when IME is OFF.
The problem seems to be that the focus remains on the cell when the comment field is displayed.
There is a person who uploaded a video, so I will include the URL.
Handsontableで日本語のコメントを書こうとするとセルに入力される現象の回避方法 #JavaScript - Qiita
If you click the comment entry field once, you can enter it, but it’s not practical.