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Big folders open in Down To The Wire and Over The Hare. A folder whose list didn't fit in 256 KB wouldn't open: clicking it did nothing. With box art, that was a little over 1,400 games, so a full set could open fine until it got its covers and then stop. Folders now open up to about 11,000 games with covers, or a Music folder of about 7,000 artists, and a folder that still won't open says why.
Covers load faster in big folders. The page fetched every cover that came near the screen and never let one go, so a fast scroll through a big folder queued up hundreds of them, covers far down the list came late, and the next folder waited behind them. It now fetches only the covers on screen, so the next folder opens at once and covers come quickly wherever you stop.
Updating from 2.2.0
On a device with Wi-Fi, MENU > System Update. Over the cable, open MENU > Down To The Wire and go to its page in a browser on your computer, which offers the update. Or with TortOS Installer 3.0.0, choose the device and Update. The games, music, saves and settings stay.
Updating from 2.1 or 2.0
With TortOS Installer 3.0.0, choose the device and Update. The games, music, saves and settings stay.
Coming from 1.x, follow 2.0.0's notes: on the Brick that's Move to TortOS 2, which installs 2.2.1.
New install
With the TortOS Installer, choose the device and Fresh install. By hand, as in the README: write TortOS-v2.2.1-brick.img.xz (Brick and Brick Hammer) or TortOS-v2.2.1-pixel2.img.xz (Pixel 2) with any program that writes disk images. Each image's -sources.tar holds the licenses and source of the open-source software in it. The Brick's GPU libraries and Wi-Fi firmware are closed and not included; its PROPRIETARY.txt names them. SHA256SUMS has the checksums of all four files.
Thanks to u/Garisaan on Reddit, for the folder that wouldn't open.
Perfection is an unattainable goal, but it's still worth aiming for.