Not sure how your proces is;
- a user types a text which is send by email
- In a microflow a text is constructed, which is send by email
In case of 1.
Download the CKEditor and use that widget as input for the user
Case 2
Create a string variable, where you will construct the message using the right HTML tags.
If you are not familiar with HTML I have a trick;
- Create a entity with one attribute, string unlimited
- create a page where you can edit a single object of your new entity
- Allow an admin to access the page and entity acces
- Add in that page the CKEditor
- Run the app, login as admin
- Go to the page, enter the text you want.
- On the top left of the editor, you can open the modus where you can view the HTML text.
- Copy paste
Done