I wouldn’t trust that article on iOS 15 jailbreaks. A lot of those is misleading/fake (e.g. Checkra1n only supports iOS 12-14, unc0ver does not support iOS 15 and unc0ver virtual doesn’t exist).

iOS 15 currently only has Dopamine and Palera1n as supported and recommended jailbreaks. Though if you only need to side load apps, take a look at TrollStore, which lets you side load apps indefinitely, but isn’t a full jailbreak (made by the same dev as Dopamine).

FYI Checkra1n isn’t that old, but there are a lot of jailbreaks that end in “ra1n” :)

What render settings are you using? Kdenlive doesn’t use Movit for rendering but rather Melt. You can try AMD VAAPI under Hardware Accelerated in the Render menu. Some other tweaks you can do include enabling Parallel Processing (for your CPU, it can go up to 8), changing Custom Quality, and changing Encoder Speed (though the last two options do affect quality so experiment with what works for you)

Related Kdenlive Documentation

Shingled Magnetic Recording

Basically the write head writes over part of the magnetic track below the current track, reducing the physical size of each data and increasing how much data can be stored on one side of a disk.They’re bad for random writes because the drive would need to rewrite data in the track below it as well.