BUFC
AB Conservative Buffer ETF
stock NASDAQ ETF

I wrote "costless" in scare quotes because there kind of is a cost, just not an upfront one. To do the buffer strategy, you buy an ATM or slightly OTM put as insurance and fund it by writing a covered call and an OTM put. You don't have to put up any additional capital this way.
The "cost" (sort of) is that the covered call caps your upside, but in practice, you can close your position at a profit and do it again, although gains would be less than without the cap. That cost may never be realized if the underlying never reaches the cap before the call expires. The benefit is that you have a buffer insuring against decline, but only to a point (that point being the OTM put strike). Even if that strike is ultimately violated, you're still ahead of where you'd be without the buffer, but you're not 100% protected.
There are many ETFs that do this strategy, or slight variations. For most of them, you need to be very careful about when you enter. You want to get in close to the buffer level so you're protected, not close to the cap where you can only lose. And then you might have to hold until the options expire to get the full protection. You'd need to check the price levels carefully before exiting. One reason there are so many of these ETFs is so that they can have different entry dates.
The one I ended up rolling into today was BUFC, which happened to be close to the ideal time having reset just a few days ago. The strikes were about where I wanted them. I didn't know it was going to be this one yesterday; I had to search for it. While I did move a lot, I'm not putting 100% in there, as I have other hedges and want some uncapped exposure.
(Not investment advice, just what I did. Your situation isn't mine. It might not be as good of a deal tomorrow. Due diligence is on you.)

I wrote "costless" in scare quotes because there kind of is a cost, just not an upfront one. To do the buffer strategy, you buy an ATM or slightly OTM put as insurance and fund it by writing a covered call and an OTM put. You don't have to put up any additional capital this way.
The "cost" (sort of) is that the covered call caps your upside, but in practice, you can close your position at a profit and do it again, although gains would be less than without the cap. That cost may never be realized if the underlying never reaches the cap before the call expires. The benefit is that you have a buffer insuring against decline, but only to a point (that point being the OTM put strike). Even if that strike is ultimately violated, you're still ahead of where you'd be without the buffer, but you're not 100% protected.
There are many ETFs that do this strategy, or slight variations. For most of them, you need to be very careful about when you enter. You want to get in close to the buffer level so you're protected, not close to the cap where you can only lose. And then you might have to hold until the options expire to get the full protection. You'd need to check the price levels carefully before exiting. One reason there are so many of these ETFs is so that they can have different entry dates.
The one I ended up rolling into today was BUFC, which happened to be close to the ideal time having reset just a few days ago. The strikes were about where I wanted them. I didn't know it was going to be this one yesterday; I had to search for it. While I did move a lot, I'm not putting 100% in there, as I have other hedges and want some uncapped exposure.
(Not investment advice, just what I did. Your situation isn't mine. It might not be as good of a deal tomorrow. Due diligence is on you.)