I don't work for MAGIX but this is what I know:
In 2012 Divide Frame wrote Spectra Layers. It was published by Sony. We assume Sony also purchased some or all of the code in addition to distributing. Versions 1, 2, and 3 were published at Sony with French coder Robin Lobel doing most of the development for version 2 and 3.
In 2016, Sony sold off various intellectual property assets related to audio software. MAGIX acquired Specra Layers and released version 4. Spectra Layers was sold standalone and bundled with Sequoia 14. Magix also released version 5.
In 2019, Steinberg acquired distribution rights. (It is assumed that this means the code and all property, but it could also mean that the coders own the IP and moved the distribution deal to Steinberg. Articles discussing that are imprecise as some of the journalists are not legal experts).
Steinberg changed the name to SpectraLayers (concatenating the two words into one), and released version 6.
Since this is a private web forum, I will share my unvarnished thoughts:
If you want to clean clicks or impulses, the built-in Spectral Cleaning by Magix is very very good. It has clear graphics, and can be opened, used, and applied in seconds. If you're a professional this really matters.
SpectraLayers is one of the most powerful restoration tools on the planet. However, configuring the display, navigating, and working as fast as you can will never approach the speed of the Magix software. If you need a click or pop, using SpectraLayers is SLOW, and complete overkill. If you need to do something complex that borders on magic/science fiction powers, you want to use SpectraLayers.
I've never disagreed with Sebastian, but this is not correct when considering SpectraLayers. The infinite adjustability of the formulae and colors to display spectral audio in SpectraLayers can be frustrating when compared to the options in SequoiaTude.
He is very right about Algorithmix and MAGIX --Those of us old enough do remember that ReNOVATOR was bundled (with a test period) inside of Magix Products. But that seems to be the extent of the sharing of underlying code.
Two versions ago Samplitude's cleaner did not have all of the features of the Sequoia version: effect % and types of crossfades/damping. Users could pay to upgrade the restoration titles to match Sequoia's. You would have to check, but I've heard the full suite is now part of the top level of Samplitude. But I'm not 100% on that.
Hope this helps.