We are migrating from SP on-prem to SP online and I have a list with a Infopath form which I was able to recreate in the "test" migration list on SP online. I have put a couple of hours on this form and I want to save it offline so I can reuse it when we do the final migration.
Could you please share a bit more about your scenario?
Do you want to save the form structure (including field structure and entered data) Offline or just the entered form data Offline?
If you want to save the form structure (including field structure and entered data) Offline, I afraid that there is no way to achieve your needs in PowerApps currently.
If you just want to save the entered form data Offline, I think the SaveDatafunction could achieve your needs. On your side, when you save your form data, you could use the If function to detect if you are online or offline. If online, save the form data back to your SP List directly, if offline, save the form data into a collection, then cache the collection into your local device.
On your side, please consider set the OnSelect property of the "Submit" button to following: