As mention in a previous post, it looks like on the ONTAP 9.9.1 install /setup documentation there are no steps to setup ONTAP 9.9.1 in ESXi. It looks like the last version to include ESXi steps was ONTAP 9.5. You should be able to deploy 9.5 and upgrade to 9.9.1 unless there has been a change in specific requirements for 9.9.1.
Thank you guys, I'll just want to make things a little bit more clear about the context 🙂
I use vsims in ESXi because at the moment, I have no beefy enough machines with VMWare workstation on 'em, and I am perfectly aware that running on ESXi since vsim 9.6 MAY work but is not officially supported.
It used to work perfectly at least until 9.7 (even VMWare tools-enabled!) so I pushed my luck a little bit by asking if someone had by any chance got a 9.9.1 vsim running on ESXi, I would have gone through regular support if I was running a supported configuration.
For "scientific curiosity", I'll try to go from 9.7 to 9.9.1 and see how it goes, I have no absolute need for it to work at the moment so it will be for fun 🙂