Each of us who have implemented Power Automate flows has had to add a flow to a Power Apps application at some point. I will show you a workaround for adding Instant flows to Power Apps solutions when this is not possible.
In the make.powerautomate.com portal, you created a new Instant flow that you would like to add to a Power Apps solution, but you can’t find it.
The image below depicts the results of your “search” when you tried to add your existing flow to the solution.
Sign in to make.powerautomate.com, find the flow you want to add to the Power Apps solution and delete it, as the image below shows.
Then add the Power Apps (V2) trigger WITHOUT making any other change and save the flow.
Now, if you search again for the flow, you will find it as shown below, select it, and add it.
To finish, delete the PowerApps(V2) trigger,
then re-add Manually trigger a flow trigger and save the flow.
And select Publish all customizations.