[Darryl Ramm]

What you are trying to do is maybe the wrong thought process. You can't upgrade memory on these Apple silicon based Macs so you should err on the side of over-configuring memory to meet future needs during the lifespan of the mac. And those future needs are hard to know.

As for what you are running now detailed calculations might not help answer future needs, you are running on old macOS, a new Mac is likely to run Ventura, with some more bloat. And Pro Tools consumption is very dependent on sessions/workload. Do you know what you will be doing in future? If updates of VIs will use more memory? And what will future Pro Tools and need? Memory use is probably going nowhere but up, nowadays even a stupid web browser can consume many GB of memory. And if you have to run under Rosetta that will add some memory use above what you would see on a native Intel machine. Some early ports of plugins to Apple silicon might be rough and need optimization etc.

If you have not been looking at memory use on multiple large sessions then maybe all you can say is you have not run into noticeable problems with 48 GB. So maybe 48GB is enough, maybe you want 64 GB on a new Mac to safe? Personally I could not think of buying a new Mac with less than 64GB, but that's me.

And what you are asking about in Activity Monitor is only part of the story, you need to also include wired memory, that's largely parts of the OS, and you need to include compressed memory. That's all then gives you an idea of how much memory is used by apps and the OS, but you also need some part of the cached files... a system without working cached files would perform like a dog. Yet it is that demand paging cache that works to fill up memory so well that it looks like all the memory is being used (it is but how well would stuff run in less memory is hard to answer). With modern demand paged operating systems if things are working OK you often don't know how things will run with less memory without just trying it... but then maybe you are heading in the wrong direction of being accurate about what you need now, on a quite different systems than what you will have in future, running different future workloads on different future software.

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And similarly I would try if possible to buy internal SSD storage (for system/boot, sessions, and samples) to meet present and future needs. No Mac Apple Silicon Mac SSD are currently upgradable, most physically cannot be, and even if you are buying a Mac Studio which have Apple proprietary socketed NAND cards, there are no third party upgradable NAND storage cards you can install in a Mac Studio today so I'd be trying to configure the very fast internal SSDs to meet my needs. They are faster than any external SSD you can add, and they are likely to be more reliable and involve less futzing around than with external Thunderbolt or USB drives, cables etc.