Hi @Anonymous ,
I was trying to do something similar. I think I managed to figure out a work around that may or may not meet your needs.
1. Use the When a new to-do in a specific folder is created (V2) trigger to create a new to-do in your Flagged Emails to-do list.

2. Use Get my profile (V2) to get your profile (if you want to assign the task to yourself).
3. Use Initialize variable to create a string that will hold the link when we parse from the JSON below. I'm naming my string variable linkToEmail.

4. Parse the body dynamic content from the trigger step using a Parse JSON step.

Here is the schema I used. I may work for you as well.
{
"type": "object",
"properties": {
"@@odata.context": {
"type": "string"
},
"@@odata.etag": {
"type": "string"
},
"importance": {
"type": "string"
},
"isReminderOn": {
"type": "boolean"
},
"status": {
"type": "string"
},
"title": {
"type": "string"
},
"createdDateTime": {
"type": "string"
},
"lastModifiedDateTime": {
"type": "string"
},
"hasAttachments": {
"type": "boolean"
},
"categories": {
"type": "array"
},
"id": {
"type": "string"
},
"linkedResources@odata.context": {
"type": "string"
},
"linkedResources": {
"type": "array",
"items": {
"type": "object",
"properties": {
"webUrl": {
"type": "string"
},
"applicationName": {
"type": "string"
},
"displayName": {
"type": "string"
},
"externalId": {
"type": "string"
},
"id": {
"type": "string"
}
},
"required": [
"webUrl",
"applicationName",
"displayName",
"externalId",
"id"
]
}
},
"body": {
"type": "object",
"properties": {
"content": {
"type": "string"
},
"contentType": {
"type": "string"
}
}
}
}
}
5. Add the webUrl dynamic content from step 4 to the string variable you created in step 3. Even though there is only one URL, it is stored in an array. So, we have to "loop" through the array and convert it to a string that we can use in the body of the planner task.

6. Create a new planner task using a Create a task step. As you can see, I'm grabbing the title from the trigger and I'm assigning it to myself using the returned value from step 2.

7. Add an Update task details step. Use the ID dynamic content from step 6 as the input value to the Task ID field. Add the variable containing the URL you created in steps 3/5 to the Description field.
8. (Optional) Delete the to-do item created by the trigger using a Delete to-do (V2) step. I don't new a to-do item and a planner task.

Warning: Step 8 will also remove the flag from the email. I haven't figured out a way around this, but for me this ins't a dealbreaker.