joomla: troubleshooting step by step for the error: 1709 Is the size of the index column too large?

I have a joomla website. After updating it to version 3.9 I started getting Error 500, unknown column & # 39; a.note & # 39; in & # 39; field list & # 39;
After trying to "fix" the problem in the extension manager, now I get
error: 1709 The size of the index column is too large. The maximum column size is 767 bytes.

Can you please help fix this?