There is a way to offer BOGO (Buy one, get one (free or at a discount)) on a product and you would need to setup the BOGO for each product you want to offer BOGO on.

The image below is how you want to set this up.
It cannot be done with percentages.
For the "working name" you want to likely enter the product ID to avoid confusion.
The "Discount Amount" should be the price of the product if you want buy one, get one free.
If you want buy one, get one half off, enter "half" the product price.

note - If you are using quantity discounts, I think it will get complicated, but may still be possible - have not tested that scenario.
I have tested what you see below, and it works fine.

Hope this helps a few folks.
Thanks,
David

Note: this requires a discount for every different price, so if you have 100 items and 90 of them have different prices, then you'll need 90 discounts.
If you have 3000 different prices, you'll need 3000 discounts and to manually keep them in sync with any prices changes that happen to products.

I think that the comment from 2017 is correct: BOGO is a popular discount structure and it would be nice to have it supported natively.

No Problems...
For a very modest fee, you can get a csv utility - https://dlss.ca/proddetail.asp?prod=Adv_Coupon_CSV
This would make short work of the whole thing.

Thanks,
David