Without plugins I added 3 user fields to the product page.
Choosing date field, text and textarea.
In cart and checkout all works fine – I see them under item name, but I don’t see them as meta fields in admin order. And anywhere else in admin order too.
Where I made a mistake in the last function?

I try do something similar to ‘product addons’, but manually. I would have few simple products, that have to be as companions. Their ids will be the same. I want to make them as checkboxes, with photo, name and price. If checkbox is checked – that product has to add to cart together with main on the product page. That’s a code, already tweaked by gpt