Unfortunately, you cannot upload the CSV directly. You need a third-party tool to convert the CSV into clickable links.
Warning: Do not use sketchy "Subscribe to all" bots that require your password. Any legitimate tool will only open the channel pages and simulate a mouse click on the subscribe button. Unfortunately, you cannot upload the CSV directly
There are three tiers to solving this problem. Tier 1 is the safest (Google Takeout). Tier 2 is the fastest (Browser Extensions). Tier 3 is for the tech-savvy (Python scripts). Warning: Do not use sketchy "Subscribe to all"
Regardless of the tool used, certain data cannot be transferred: There are three tiers to solving this problem
Authentication: OAuth tokens for YouTube; store tokens only for session duration; refreshable tokens optional with explicit consent.