Youtube premium add songs from playlist to your liked songs

youtube-music-multi-add.md

Open your playlist in your browser, scroll all the way to the bottom (Youtube music does not show all at once), open your developer tools, run this in the console:

(async () => {
  const buttons = document.querySelectorAll('button.ytSpecButtonShapeNextHost[aria-pressed="false"][aria-label="Like"]');
  console.log(`Found ${buttons.length} Like buttons to click`);
  for (const btn of buttons) {
    btn.click();
    await new Promise(r => setTimeout(r, 500));
  }
  console.log('Done');
})();

It will add all the songs in the list to your liked songs.