I'm cleaning up a 25-30 year old bicycle. First time I've stripped one almost right back to the frame.

Strongly recommend the rust remover described by Backyard Ballistics[0] on his second channel[1]; 1 liter water, 100g citric acid, 40g washing soda, generous squirt of dish soap. He claims the acid and alkali cancel out so there's nothing to attack the normal metal surface, but they leave citrate ions which dissolve rust by chelation, which makes it better than just citric acid, vinegar, or soda alone, which all pit and dissolve the clean metal surfaces, and easier/better than wire wool scratching. He also claims it's as effective as EvapoRust but much cheaper and can do more rust dissolving per litre than EvapoRust.

[0] https://www.youtube.com/@Backyard.Ballistics - restoration of old and very rusty guns

[1] https://www.youtube.com/watch?v=fVYZmeReKKY - "The Ultimate HOMEMADE Rust Remover (Better than EvapoRust)", Beyond Ballistics channel