The short answer
No, not a real Kali Linux install — not without jailbreaking, and jailbreaking comes with its own real security and stability trade-offs. iOS's sandboxing is specifically designed to block the low-level system access a full Linux distribution needs, and that's true no matter which app claims otherwise.
What apps like iSH actually give you
iSH is the closest thing that's genuinely available on the App Store: a lightweight Alpine Linux userland, running under x86 emulation, inside Apple's normal app sandbox. You get a real terminal and a real package manager (apk) — but it isn't Kali, it doesn't have root over the device, and because it's emulating an entirely different CPU architecture, anything heavier than basic scripting gets slow fast.
Why Android + Termux is the closer match
Termux runs natively on the phone's actual ARM processor — no emulation layer — which is the whole reason projects like Kali NetHunter and community Termux-based Kali installers are built on Android, not iOS. If the actual goal is a real Kali-style toolset on a phone, that's the realistic path.