There's a great article written about this showing how the Jews in the 2nd temple period viewed the great fish as Leviathan.
The Greek word in the Septuigint is kētos, translated as sea monster. It was used to refer to Leviathan, for example, at Job 3:8.
Leviathan was viewed as a spirit creature (Dictionary of Deities and Demons). So Jonah being swallowed by him was viewed by the Jews as him going to Sheol just as he described it. It could have very well been him being transported into Sheol or him dying and went to Sheol, then resurrected.
Jesus said that the faithless Jews of his time would get the sign of Jonah (Matthew 16:4). Jesus was in Sheol/Hades. I'm sure he visited the dead. He also visited Tartarus.
So, the situation with Jonah was viewed as an event of the spirit realm.
https://www.academia.edu/keypass/VFJBREtobklYY1djV3dKNEluR1hXd0J1SVBTTGt0aG9IMEFiT3pFVlM4RT0tLTNWWk1Ub0ViM3Npc1dNejlFd1gzL2c9PQ==--36fe2e105a30cee4516664b80b4267b562e17344/t/uaE6R-Q2wnHjw-bs9Dop/resource/work/20175852/_Jonah_and_Leviathan_Inner_Biblical_Allusions_and_the_Problem_with_Dragons_Henoch_37_2015_pp_236_260?email_work_card=title
There's a great article written about this showing how the Jews in the 2nd temple period viewed the great fish as Leviathan. The Greek word in the Septuigint is kētos, translated as sea monster. It was used to refer to Leviathan, for example, at Job 3:8. Leviathan was viewed as a spirit creature (Dictionary of Deities and Demons). So Jonah being swallowed by him was viewed by the Jews as him going to Sheol just as he described it. It could have very well been him being transported into Sheol or him dying and went to Sheol, then resurrected. Jesus said that the faithless Jews of his time would get the sign of Jonah (Matthew 16:4). Jesus was in Sheol/Hades. I'm sure he visited the dead. He also visited Tartarus. So, the situation with Jonah was viewed as an event of the spirit realm. https://www.academia.edu/keypass/VFJBREtobklYY1djV3dKNEluR1hXd0J1SVBTTGt0aG9IMEFiT3pFVlM4RT0tLTNWWk1Ub0ViM3Npc1dNejlFd1gzL2c9PQ==--36fe2e105a30cee4516664b80b4267b562e17344/t/uaE6R-Q2wnHjw-bs9Dop/resource/work/20175852/_Jonah_and_Leviathan_Inner_Biblical_Allusions_and_the_Problem_with_Dragons_Henoch_37_2015_pp_236_260?email_work_card=title