Importing Subscriptions from YouTube
Open
takeout.google.com/takeout/custom/youtube
In "Select data to include", click on "All YouTube data included" and select only "subscriptions".
Create the export and download the zip file.
Extract subscriptions.json from the zip file.
Select and import the file above.
Importing Subscriptions from Invidious
Importing Subscriptions from NewPipe
Go to the Feed tab.
Click on the arrow on where it says "Subscriptions".
Save the file somewhere.
Select and import the file above.