There is no native "Export/Import" button for subscriptions inside the YouTube app. To do this efficiently, you need to use a browser on a computer (Chrome, Firefox, Edge, etc.). Mobile apps will not work for this method.
Even with these workarounds, the following : youtube subscription transfer
Several community-built extensions automate the process after you export your list: There is no native "Export/Import" button for subscriptions
Copy the URL of your old channel and visit it while logged into your new account . youtube subscription transfer
Google Takeout is the official way to download your data from any Google service. Here’s how to use it for subscriptions: