You're overthinking this way too much. By your own admission, you are a novice cyclist, yet you are going into the minutiae of things like 105 groupsets and carbon frames! Your list of "requirements" in terms of spec is pointless because you have nothing to compare them with. I've been riding bikes for many years and none of mine have 105 or disc brakes, and none are carbon framed either. Strictly steel only, and rim braked. No-one "needs" discs any more than anyone "needs" Tiagra as a minimum. It's all marketing spin. What you do REALLY need as a commuter above all else, is a bike that will still be where you parked it in the morning, when you come back to it at the end of the day to go home on! So lose the vanity attitude and forget about anything expensive/pretty/bling and instead go for something that looks dull/boring/scruffy/worthless, so it is not remotely attractive to bike thieves. That way you stand the best chance of being able to ride home rather than have to walk because your bike has gone missing......
Once you've mitigated theft risk, the next things are durability and practicality. Some (super-fit) people will tell you to commute on a stripped down fixie/single speed because it offers a "pure" cycling experience and minimal maintenance. Ignore them. Someone like you needs a good range of low gears. I'd suggest you get a bike equipped with a 28/38/48T triple front chainring. That means an old rigid MTB, Hybrid, or Tourer in practice, not a weekend warrior's road bike. You also need the ability to run decent stout comfortable tyres AND have mudguards on at the same time. A lot of bikes can only fit sensible tyres if run guard-less, and if guards are fitted the size that will fit drops down by several mm. It's bonkers to even consider any bike without decent tyre clearance for utility riding all year round. You also need proper, puncture resistant tyres like Schwalbe Marathons if you don't want to be late for work because of flats. Tyres with a high level of puncture resistance tend to be taller than lightweight roadie tyres, and so limit mudguard/frame clearance more still. Much of the UK's roads and canal paths have one thing in common, the surface is in poor condition and can be rough. Forget narrow high pressure tyres, go for 32 or 35mm as a minimum..
A lot of modern road bikes do not have provision for racks and guards, because they are designed with appearance in mind, not practicality. Years ago, clubmen's sports bikes did have these features, because they were often ridden all-year round, or to get to work on in the week, as well as weekends. Cyclists were practical then. Many modern roadies are way too vain to even have mudguards mounts let alone actual mudguards on their bikes! Leave them to pose in their Lycra, and get yourself a practical flat bar hybrid or drop-bar touring type machine. Secondhand is way better value than buying new, sometimes you can pick up really nice bikes for literally a tenth or less than their original cost - which can be very low mileage, having spent years in someone's garage not even getting ridden and worn out.