You can do that too, use an Android VM. Whichever way works best or works easiest for you.
I use Whatsapp in that exact scenario that you are describing. It's an old Android phone connected to wi-fi and the phone is never touched for anything outside of Whatsapp.
Having it setup that way, or for you with FB/IG, if there is no SIM in the phone, do not install anything else, no contacts in phone, you can effectively use it anonymously.
I suggest you use an Android phone so you can download APK files to install, disable Play Store and similar network services, and maybe once a month download the lastest APK and install to update it. I do that for Whatsapp or updating since I have all Google services disabled on the phone.
Voyager is on both platforms, Jebora is only for Android, both are pure open source so you have full privacy and anonymity.
Pay to start a company, then pay to hire a few people, and see what you think of how expensive it is to hire someone and if it's worth the cost out of your own cash.