Some diesel additives claim to increase cetane rating, in addition to adding lubricity. How much it helps, I don't know.
This is what I have been using for most of the past 2000 miles in the motorhome because it sat so much and I wanted to clean up the IP and injectors:
https://www.howeslube.com/products/meaner-power-kleaner
It doesn't claim to add cetane, but it claims to clean injectors and adds lubricity.
I may switch back to buying Power Service Diesel Kleen though, since it does both of those plus claims cetane boost. PS costs more per dose but eh. I used PS in the truck except last winter some when I was using Howes for antigel.
Since we pretty much NEED to use an additive to help with lubrication, we may as well use something that claims to boost cetane too when we don't need antigel.
I don't think antigel is worth bothering with for me most of the time. I think only once did I see my fuel gel any and that was a couple years ago when it got down to around 7 degrees one morning. I had antigel in it and I never had a problem starting the truck. It has a clear plastic fuel filter just before the tiny electric fuel pump and it looked cloudy when it got down that cold.
Usually I don't see temps that low though. I have been sticking around the Texas area of the country in winter.