Hi Igor and team,
Hope you guys enjoyed your vacation. I will also take this opportunity to wish you all a very happy, healthy and successful new year (hope it is not too late :-)
Regarding the issue, I differ with what you are saying that deals without old new prices are useless. It is not necessary for an offer to always have an old or new price. Offer (deal) can simply be an affiliate link to offer page on merchant's website but it will not have any coupon code available.
For example, on see on page https://couponsathi.com/store/tatacliq-coupons/ it has both offers without coupon code (categorized as a deal) and also offers having coupon codes (categorized as a coupon)
So if I click on Coupons filter the theme is correctly filtering coupons but if I click on deals filter deals are filtered.
I am not bothered currently about Sale filter where I feel Old and New Prices make sense.
Either Deals or Sales Filter should filter such offers (without coupons and old new prices)
Now if you some of the well-known coupon sites in India you will find such filters. Examples below for your reference.
Some of the other themes eg PremiumPress also has such a functionality.
I hope I am able to explain the issue correctly. Hope for your quick reply.