メッセージセンター(MC295027)によると、Plannner のプランにあるメモにリッチテキストが利用可能になるそうです。対象は Planner(Web) と Teams アプリで、iOS、Android、SharePoint 等で Planner については後日展開になります。
リッチテキストが利用できることで表現力があがります。文字に書式を設定したり、画像の挿入ができたり。ただ、残念ながらコメント欄については対象外で、従来通りテキストだけになるようです。
以下、メッセージ全文です
We are adding support for rich text (bold, italics, underline, etc.) and images in the Planner task notes field. NOTE: We will update this post once we have Microsoft Graph documentation for the new rich text task notes field available. This message is associated with Microsoft 365 Roadmap ID 85688.
When this will happen:
We expect to begin rolling out the new rich text task notes field in late March (previously mid-February) and we expect to complete the rollout by mid-April (previously late March).
How this will affect your organization:
To support this capability, we are introducing a new rich text enabled task notes field in the Planner Microsoft Graph API. This will result in two task notes fields in our API – the new “rich text task notes field” and the existing “plain text task notes field.” When this feature launches, Planner for the Web and for Teams (Tasks app) will support rich text in task notes. Other Planner experiences in iOS, Android, SharePoint, and Power Automate will only support plain text task notes, but we plan to update these apps to support rich text at a later date.
When this feature update is deployed, all existing task notes content will be preserved in the new rich text enabled task notes field, so users will be able to continue viewing and editing notes without interruption.
We will maintain compatibility between the rich text task notes field and plain text task notes field by ensuring both fields’ contents stay in sync.
If a user edits the rich text task notes field, all content is synced to the plain text task notes field automatically. Any rich content is converted to plain text and synced to the plain text task notes field.
If a user edits the plain text task notes field via the Microsoft Graph API or via a client which only supports the plain text field, the contents in the plain text task notes field is synced to the rich text task notes field without modification. Therefore edits to the plain text task notes field will result in the removal of any pre-existing rich text, text formatting, or images in the rich text notes field.
If a user chooses to insert images in the rich text task notes field, a preview of the image will appear in the task notes field. End users should not see any interruption in their Planner experiences. They can continue using task notes as they do today but gain the ability to insert rich text and view image previews in task notes if desired (for Planner experiences which support it).What you need to do to prepare:
If your organization has custom applications interacting with our Microsoft Graph Planner API, make sure to update the apps to support the rich text task notes field as soon as it is available to take advantage of the new notes capabilities. We will maintain support for the existing plain text task notes field in our Microsoft Graph Planner API for at least 36 months. If your organization has applications or workflows which parse the task notes to trigger logic based off contents in the notes field, we recommend users continue to input only plain text in task notes and not apply text formatting or insert images into task notes. Such apps should also be updated to avoid parsing task notes or applying logic to contents in the task notes as these are not recommended uses of the task notes field in our API.
ちょっと気になるのはメモ欄を参照するフローですね。データー形式が変わるため、フローによっては（特定の文言をひっかけている場合など）正しく動作しなくなる可能がりますので、注意が必要かもしれません
