I last did an App Store deployment in 2019… so please keep this in mind.
The easy answer to your original question is that there is no special privilege that comes with the SBA program in regards to iOS distribution. Apple's App Store has nothing to do with Claris. You will need to apply for the FBA and the SBA with Claris. You will need to create a developer account, an App Store account and perhaps enrol in other programs (such as the Enterprise Program) with Apple.
We tried the v18 SDK shortly after FileMaker 18 came out. We ditched it fairly quickly… because of the background location entitlement issue. I am guessing the issues have not been resolved with the v19 SDK based on the comments I am reading… so if the v17 SDK works for your solutions, I suggest you use it.
Remember that Claris discourages distribution via the App Store. As such, all calls to Claris for help fell on deaf ears back then. The entitlement issues was only one of the reasons. Claris and Apple do not approach development at all in the same way. That said, the Enterprise Program solved our distribution problems because Apple is much more lenient about breaking its rules when it comes to enterprise distribution.
We found that the key to easy distribution was to stick to free apps. Our customers would pay us directly. We would supply them with an App Store redemption code (obtained via the Enterprise Program) and they would "pay" for the app with the redemption code. That said, each user would have its own redemption code.
We preferred this route over MDM pretty much for the same reason you mentioned… and also because updates were very easy to push to users.
Hope this helps.