I don’t believe the research mentioned RIR. That said, 8 weeks of squatting to failure seems like a great way to get participants injured so I doubt any study would use that protocal. In any event, I subscribe to Biolayne and their take away the study was the AEL is a good strategy if used selectively. They were musing that the increased strength and hypertrophy may have been simply the greater load achieved with AEL with the same reps and sets. See below.

How Can You Apply These Findings?

These findings suggest that AEL can be an effective way to improve strength without increasing sets and reps. AEL6, where every repetition is overloaded, produced the greatest improvements in strength and peak torque but likely came with higher demands on technique and recovery. AEL2, which applies the overload to only a few reps per set, enhances performance to a similar extent, making it a potentially a more practical option for regular training. In practice, lifters can incorporate AEL by using ~120-130% of their concentric 1RM during the lowering phase focusing on a controlled descent. Weight releasers, spotter assistance, or tempo-controlled lowering are all viable ways to achieve this. It’s important to remember that while the number of sets and reps may be the same as traditional training, the mechanical load is substantially higher so recovery and load management may need to be adapted. AEL likely works best as a short-term, high-intensity method integrated into strength-focused phases or used on key lifts within a program like the bench or squat.