Notability recently moved to a tiered model, making it more accessible without the need for illegal downloads.
If you have a legitimate IPA file and want to install it without the App Store, you can use safe sideloading tools. This does not "crack" the app but allows you to manage your own software.
: An open-source project that allows users to refresh app certificates over Wi-Fi, preventing the app from expiring every 7 days. Summary of Notability Tiers Key Features Starter Unlimited notes, basic tools, cloud sync. Plus/Pro Subscription Handwriting recognition, math support, live transcription. swaggyP36000/TrollStore-IPAs - GitHub
Searching for "cracked" or "free download" IPAs often leads to unsafe websites.