Use a good high-quality Multi Vehicle ATF and don't monkey around with additives. It is important to do a complete ATF replacement if you change brand or formulation. If you do that, it is also important to reset the adaptive values and trigger a re-learn and follow the steps outlined by the computer.
You can use one of these devices to do that:
Link:
https://www.amazon.com/dp/B0BZ4L25CZ
View attachment 161520
It's $100+tax on Amazon (after $50 off coupon, click on it). After you get it, hook it up to WiFi, update everything from Settings, and purchase the package for your Vehicle Manufacturer, it's $60. Well worth the money. You will have bi-directional access to every module in your vehicle.
That's the right way to do it. Now, if you want to waste time and money playing with additives, that's up to you.
I tried Lubegard Red in our 2017 Hyundai Santa Fe. It softened the shifts a tiny bit when mixed with Red Line D6. I use 20 oz of it. I didn't do anything of substance. In the end, what improved my shifting tremendously and fixed my 1-2 shifting issue was to switch to Mobil 1 LV ATF HP and reset the transmission computer. Now my transmission is shifting flawless, better than when it was new.