Provide the option to permanently "dock" the Dynamic Content box on the side of the window.
See sample mockup below:
This idea could be extended into a click-and-drag interface. The way this would work is that instead of clicking on a field and waiting for the dynamic content to populate, you would simply drag fields from the dynamic content window straight onto the appropriate fields.
This solves several small yet annoying issues with working with the dynamic content window.
1. Whenever you click on a new field, the dynamic content window resets, so you must search for where you were again. This is particularly annoying when you are updating a sharepoint list item that has many fields.
2. When clicking on a new field, the positions of several things shift, which is bad user experience: position of the add dynamic content link, the positions of all fields below. This tends to happen about a second after clicking on the field, which makes it all the more frustrating if you are rapidly clicking through fields and must first wait.
3. When dealing with large text fields that might take up more than one screen (such as large email formats or json), you have to constantly scroll up to where you want to insert the dynamic content, select the position with the cursor, scroll down to the dynamic content box and insert, scroll up again, repeat. This is slow and can be very frustrating.
Additionally, this could improve other aspects of Power Automate that have been implemented poorly:
4. Small size of custom expression box. With the content window docked on the side, this input box can be increased both horizontally and vertically (allow multiple rows of text) which will make editing custom expressions less of a nightmare to work with.
5. More space available to provide reference for custom expressions.
6. More space to provide better filtering capabilities for custom content, for example filters on which actions to include and which data types to include.
The small pop-out dynamic content window is great for small flows that only contain one or two actions. For anything bigger it quickly becomes unmanageable.