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” :)