Assuming you mean Quantitative Reasoning (the math section) - yeah, OG alone isn't enough if you're hitting a ceiling and need more detailed explanations.
OG gives you official questions and that matters a lot for calibration, but the solutions in the book are often pretty thin. They'll show you the answer but not why wrong choices are tempting or what trap the question is setting.
What actually moved the needle for me on Quant in the GMAT Focus was pairing OG practice with deep error analysis. Every time I got a Problem Solving or Data Sufficiency question wrong, I'd try to figure out not just the right method, but what exactly I assumed incorrectly. That's where growth happens.
For additional resources: the GMAT Club forum has detailed community explanations on basically every OG question, and those threads often surface the common traps. The Math Book pinned in the Quantitative Questions section is also solid for brushing up on specific concept areas (Number Properties, Fractions, Percents, etc.).
YouTube-wise, I'd be careful about channels that teach old-style GMAT math. The Focus Edition skews harder and weirder on Quant, so you want content made for the current format. That said, concept explanations for things like mixture problems or work-rate questions translate fine across formats.
One thing I found genuinely useful: once you've done a batch of OG problems and reviewed them, do a timed set of questions at your weak tag. GMAT Club lets you filter by topic and difficulty. That targeted drilling is where OG practice really compounds.