My The alarm clock on my mobile rings at 8:45.

Not wrong, but this is a little more natural. It's on your phone, so it's clearly your alarm clock.

Compare "check my messages" and "check the messages on my phone".

I like to wake up slowly, so I listen to the radio, and after a while I check my phone concerningfor messages and my daily tasks, which I administratmanage in a gamification app.

The basic meaning is right, but "administrate" sounds very much like you are overseeing a lot of people, or a complex system. Here it's excessive.

Between 9:15 and 9:30, I reactually get up and prepare our breakfast, while my husband does his trainingworks out on the crosstrainer.

I suggest "actually get up", as it's a natural way to imply that you finally completed a partial attempt to get up. "I 'get up' at 9, but I only actually get up at 9:30".

"really get up" does work. "completely get up", "fully get up", "get completely up".

"training on the crosstrainer" is correct but sounds awkward. To a native, of course you're training on it - it's a crosstrainer, that's what it does :) so specifying that you're training is unnecessary, and you'd probably just say "goes on the crosstrainer" or "uses the crosstrainer", if you didn't want to come up with another verb to be more specific about what you were doing on it.

Sometimes, I have an egg on toast, sometimes some spelt pops with milk and honey, but most of the time I eat toast with jam or chocolate and a vanilla quark (which is a special kind of dairy product, a bit like skyr).

Quark, skyr, yoghurt, cheese - in this context they're all uncountable. "A pot of vanilla quark".

"a kind of dairy" is awkward possibly for the same reason, but it's a strange word and I'm not sure. Adding "product" turns it into "dairy product", a word that is completely regular and behaves much more nicely.

In the UK at least, you can just "have egg on toast". But an egg on toast is fine and perfectly safe.

If I don't have any peaches or nectarines, I drink a glass of apple juice, diluted with water.

This is subtle and I can't explain why, but I would definitely say I "don't have any". Even if I only need one. Your sentence is grammatical and clear, but a slightly strange way to say this in this context.

My alarm clock on my mobilphone rings at 8:45.

I like to wake up slowly, so I listen to the radio and a. After a while, I check my phone concerningfor messages and my daily tasks, which I administrateset up in a gamification app.

Between 9:15 and 9:30, I reactually get up and prepare our breakfast, while my husband does his training on the crosstrainer.

Sometimes, I have an egg on toast, sometimes some spelt pops with milk and honey, but most of the time I eat toast with jam or chocolate and a vanilla quark (which is a special kind of dairy, a bit like skyr).

Wow, I never knew what spelt pops were until I had to Google it just now!