Convert DEB to IPA

The main reason why someone is looking for deb to ipa conversion is potential use of Linux apps to jailbroken iOS devices. Debian's DEB format is of interest, because it is the default format used in Cydia, which is popular package manager used on jailbroken iPhones and iPads, allowing users to install software and modifications that are not available through the Apple App Store.

Cydia primarily uses the DEB Packages for its applications and tweaks. On jailbroken iOS devices, users can directly install .deb files using Cydia, bypassing the need to convert them into .ipa files. So the real deal is actually to prepare .deb files that can work with Cydia. This is not a task for a simple file converter thought and there a not even standartized tools or procedures how to convert deb to ipa, simply because of different nature of various apps and programming environments.

Does some kind of deb to ipa converter even exists?

No such app exists. You will never find app that can be used for this, or any utility that can automate the process of converting Linux apps for Cydia. It always requires manual programming work in Xcode or similar IDE and the long process of building Debian package.

In short this process requires iOS development knowledge, familiarity with Unix/Linux command-line tools, and a good understanding of the iOS file system and jailbreak ecosystem. It's mostly undertaken by experienced developers.