Q- The statement ليعبدون اي ليعرفون is attributed to Sayyiduna ‘Abdullah ibn ‘Abbas (radiyallahu’anhuma) with regards to the meaning of وما خلقت الجن والإنس إلا ليعبدون . Is this attribution sound?
This has been cited in the following tafsir books as the tafsir of Mujahid (rahimahullah), who is the student of Sayyiduna ‘Ibn ‘Abbas’ (radiyallahu’anhu):
1. Tafsir Baghawi,
2. Tafsir Qurtubi,
3. Ruhul Ma’ani
4. It has also been recorded in Tafsir Ibn Kathir from Imam Ibn Jurayj (rahimahullah) who is a Tabi’i.
The tafsir of Sayyiduna ‘Abdullah ibn ‘Abbas (radiyallahu’anhuma) for this verse is quoted as:
ليقروا بعبادتي طوعا أو كرها
(Tafsir Tabari & Ibn Kathir, Surah Dhariyat, verse: 56)
could not locate the explanation in your question as that of Sayyiduna Ibn ‘Abbas (radiyallahu’anhuma).
And Allah Ta’ala Knows Best
https://hadithanswers.com/tafsir-of-ibn-abbas-on-the-verse-of-surah-dhariyat/