In one of your posts, you also emphasized that devas and Brahmas who reach the arahant stage automatically enter Parinibbānna. Their bodies are too thin to live as arahants.
In the point 14.
“Thus, the fine body (trija kaya) of the gandhabba cannot “bear” the energy associated with an Arahant. See “gandhabba (Manomaya Kaya).”
In the same way, the invisible, subtle “bodies” of a Deva or a Brahma also cannot sustain the mind of an Arahant. Thus, if a Deva or a Brahma attains the Arahanthood, they will immediately attain Parinibbāna. In other words, there are no living Arahants in Deva or Brahma realms.”
Nibbāna “Exists”, but Not in This World
To draw another parallel. In the suttas, there are stories where Lord Buddha and other arahants transfer merit to apaya beings like petas (hungry ghosts). As a result of these transfers of merit, they die and are reborn as devas.
AN INTRODUCTION TO PETAVATTHU: STORIES OF HUNGRY GHOSTS
ARAHANT IN THERAVADA BUDDHISM.
“it is reported that because the lay life could not properly support the life of an Arahant, one who becomes an Arahant as a lay person should ordain as a monk on the same day or pass away”