Hi partner,
This is by design.
When you enable "Enable rich text notes in Timeline" in the system settings, all notes created after enabling it will contain HTML-Syntax.
If you disable "Enable rich text notes in Timeline", the newly created notes afterwards will not contain HTML-Syntax.
For the notes that already contain HTML-Syntax, we can only delete their HTML-Syntax manually. Microsoft will not provide the function of automatically deleting HTML-Syntax, because this may cause the consequences of deleting data by mistake.
The following is a comment from the Microsoft support engineer on this issue.
"Reports will always display the html tags for records that were created when rich text notes was enabled until the customer removes them from the source records. If you have rich text notes enabled and create 10 notes and then disable rich text. And create records 11-20. When you export out the description for notes 1-20 you will see html tags in 1-10 and no html tags in 11-20. It is the customer responsibility to remove the html tags (either in the source or in the report processing).
The rich text notes for timeline was introduced in April 2020 Wave 1 - https://docs.microsoft.com/en-us/dynamics365-release-plan/2020wave1/dynamics365-customer-service/rich-text-notes-keyword-search-timeline. The ability to enable or disable rich text notes is documented at https://docs.microsoft.com/en-us/powerapps/maker/model-driven-apps/set-up-timeline-control#enable-or-disable-rich-text-editor-for-notes-in-timeline. When the customer disables rich text any notes that have been created while rich text was enabled will continue to have the html tags since that is how the rich text formatting is rendered. It is the responsibility of the customer to determine the best strategy for removing these html tags. We don't remove the html tags because our assumptions of data removal could result in data loss.
Once you have disabled rich text notes, the subsequent notes that are created will no longer have any formatting and therefore you will no longer encounter html tags in exported data. However, you will need to come up with a strategy for removing the tags from any of the notes which were created while rich text was enabled."
