Yet another sizing question

Here’s yet another bike sizing question, but from a slightly different angle.

To start off, I’ve zero experience with road bikes, but decided it’s time to get one. Where I live there’s like one bike fitting service in the most expensive bike shop in town, that comes with a price tag not meant for regular people to even consider.

When looking at the bike sizing tool for some Canyon models I’m given this picture, which suggests that I go for a size M, based on my inseam and height.

But here’s the catch – having seen quite a bunch of YT videos from professional bike fitters and the like (Cade media, bikefitjames, etc) – they’re all saying that these two measurements mean pretty much nothing, much like any manufacturers’ suggested sizing charts. With this bikefitjames fella even saying that the proper size for a Canyon road bike is actually one or even two sizes down from what their online tools suggests.

By looking at the chart, the inseam size doesn’t really even matter as much for me. That’s not to mention that it’s different for every time I take a measure and is highly dependent on how deep I shove a book up my behind, ranging from 81 to 85 cm.

But with all this abundant YT bike fitting information in mind – does anyone have any real practical advice which frame size to go for? Should I stick with the suggested size or go one down?