ASUS ROG Ally Optimized Settings
On the ROG Ally, the only way is the 30 FPS way. Setting most settings to "low," Textures to "medium," Texture Filtering to "high," resolution to 900p, FSR 2 to "performance," and enabling SSAO results in an average performance that can go as high as 40 FPS+ and as low as the 20s when huge hordes of enemies are rendered on-screen. The 25 W power profile (30 W when on charger) is a must, of course, which means you will get about an hour or less of playtime with a full battery.
If you want to game longer without needing to hook your Ally to a charger, set the resolution to 720p, everything aside from textures and Texture Filtering to "low," and FSR 2 to "balanced" or "performance."
Then, select the "Manual" power profile and start bumping the TDP value from 16 W upwards until you arrive at a value that gives you playable enough performance. This will prolong battery life to about an hour and a half, perhaps longer if you consider a cinematic frame rate—24 FPS on average—playable.
Lastly, you can utilize Lossless Scaling to bump the average frame rate if you're fine with extra latency and frame generation artifacts.