Hi @Marcormark !

On which criteria Deezer categorize discography I don't know and in this moment Featured in is no longer available on Deezer .

On web I found definition of the different release types :

1. Standard album

Standard albums are long-play releases of an artist or band which contain original tracks. Until the mid-80s, they usually came in LP (vinyl long play record) format. At least since the 90s, the common form of release is a CD (compact disc). Other formats include cassette, 8-track tapes, and more recently minidisc, DVD-A, mp3, etc.
Single albums usually have a playing time of at least 28 minutes. Standard albums can be published alone, but also in double, triple, or more record sets. A standard album contains original, previously unpublished material of that artist or band. An exception to this rule is made for albums that are released for the first time as stand-alone releases when they were previously available as part of a compilation box set or as a bonus disc (examples like this include Static Age https://deezer.page.link/qeZub4kGq3GGnqPZA  and Live Nassau Coliseum '76  https://deezer.page.link/B3v9gSRX8AVVpnS27 ). As a general rule, the songs on a standard album should only appear once on a single primary standard album and should not be duplicated over multiple primary standard albums.

The term standard album also spans live albums (albums that contain live recordings) as long as these particular live recordings have not been published before.

2. EP / Mini-albums

An EP (or Extended Play) release is a musical work that is too long to qualify as a single and too short to qualify as an album. It is commonly known to contain between 4 and 7 tracks, but there are often exceptions that run either way. Some EPs run 40 minutes or more, and some contain only 1 or 2 tracks.

Similarly, it is important to note that Singles are not restricted to 2 or 3 tracks and can often contain as many as an EP. What makes a single a single is a track that acts as the focal point of the release. So, it is not uncommon for a CD single to have more than one B-side. Having five B-sides does not automatically change its classification to an EP. For example, a CD with ten remixes of the same song is still considered a single. Likewise, a release with one studio track (the single) and four live B-sides should still be considered a single.

A release should always be categorized as an EP if it is specifically written on the release or if the official artist or label site lists the release as one.

When adding an EP to the database, be sure to enter the title of the release faithfully. Do not add "EP" or "E.P." to the title unless indicated as part of the title on the release.

Mini-albums should be filed under EPs.

3. Compilation

For our purposes, the definition of a compilation is a recording whose primary content is music that a particular artist or band has previously released. Most prominently, these are so-called "Best of" or "Greatest Hits" publications, "B-sides" collections, or collections of previously-released material by various artists organized around a time period, genre, or other common thread. But there are also other forms (i.e., box sets) where the tracks of a compilation have been published before.

A release is a compilation when more than 50% of its material has been previously released. Note that songs released on singles and EPs up to 12 months prior to the release do not count towards the % of previously released material. This exception does not cover when multiple entire EPs are being compiled together, like

13 Songs  https://deezer.page.link/mRDkRbLg54e58rT79 or 

The Three E.P.’s  https://deezer.page.link/62cJD5T6RiYMmoP4A

The 50% can be calculated by the number of tracks or length; in debatable cases, it's better to reach a consensus for the release via the site policy board.

A various artists release that includes material that had not been previously released is not a compilation .

Note: Re-releases of two full-length albums on one compact disc should be entered as compilations as well. This kind of release is clearly differentiated from a regular reissue and often displays the cover art of both albums.

4. Single

A single is a musical work by an artist that is typically formed by a collection of two to three tracks, first known in the vinyl world as a 7" at 45RPM, and later at 12". Along the way, the term single has been applied to limited-length cassettes and compact discs.

5.Live albums

Live albums are releases consisting entirely of live music which is previously released .
If music are previously unreleased then is categorized as Standard Album.

sourceRYM

Thank you, that's huge! 
However, maybe it is not exactly what I was looking for, because I think Deezer has specific criteria that may or may not be the same or similar to the most common definitions.

I forgot to point out the "Featured in" section still works on the Android app, so we can not say it is no longer available on Deezer, because that would not be the truth!

@Marcormark !

in this moment Featured in is no longer available on Deezer

(when I answered, it was not available at that moment, but NOW is available .

Yes, I know, thanks, but not for all artists and it still does not work neither on Desktop nor on the web browser version as it should:
https://en.deezercommunity.com/other-devices-49/web-version-featured-in-no-longer-visible-78599?postid=238032#post238032