https://en.wikipedia.org/wiki/Oncotarget
"In 2018 Clarivate delisted the journal from the Journal Citation Reports and all of its other products because "the journal no longer meets the standards necessary for continued coverage","
From your reference:
“The journal is abstracted and indexed in Index Medicus/MEDLINE/PubMed[1] and Scopus. In 2022, it was re-indexed by Index Medicus/MEDLINE[3] after being dropped in 2017.”