As iI mentioned in my last message, iI left my previous job and recently started a new one.

The word "I" always has a capital letter.

It's been almost a week since i joined, and i'aI'm really enjoying it.

"I'm" is the abbreviation of "I am". The apostrophe replaces the space and the a.

I'am currently in the onboarding proccess and iI've been noticed a few things about it.

"onboarding" -> starting at something (usually/especially a job)
"boarding" -> getting on a large vehicle (especially planes and boats, sometimes buses and trains)

The biggest change is iI feel thea sense of freedom, iI mean there is aare flexible working hours in contratst to my previous job thas at had strict working horurs.

I have more home office oportunitesopportunities to work in my home office, its a litibtle bit strange but iI have to fit into this situtation.

Started the (a) new job

Maybe "a new job" instead of "the new job". "The new job" would work if you already talked about this new job in one of your previous essays.
Both is fine though.

As iI mentioned last message, i left my previous job and recently started a new one.

Ah, I see. "The new job" in the title if fine then! :)

It's been almost a week since i joined, and i' (the company / workplace), and I'm (OR I am) really enjoying it.

You can't "join" a job. You have to join something more specific - like a firm/company or a workplace.

I'am currently in the boarding proccessprocess of transferring to the new workplace (or job) and iI've been noticed a few things about it.

"Boarding" doesn't work well here. Boarding refers to "boarding on a plane" or a bus.

TI feel the biggest change is i feel the sense of freedom, i. I mean there is are flexible working hours in contratst to my previous job has a, which had strict working horurs.

I have more home office opportunities, it for working from home. It's a litibtle bit strange but i have to fit this situtationmake it work somehow.

Better as two separate sentences.

Started the na New jJob

As iI mentioned in my last message, iI left my previous job and recently started a new one.

It's been almost a week since iI joined, and i'aI'm really enjoying it.

"I'm" or "I am", never "I'am"

I'am currently in the onboarding proccess, and i've beenIve noticed a few things about it.

Generally (at least in the UK) we call the period shortly after joining a company the "onboarding" process

The biggest change is iI feel is the sense of freedom, i. By which I mean there is aare flexible working hours in contratst to my previous job has awhich had strict working horus.

Since "working hours" is plural, you should use "are" instead of "is".
"strict working hours" is maybe a little strange, "fixed working hours" might be a better replacement.

I have more home office opportunities, it to work from home. It's a litibtle bit strange but iI have to fit this situtationadapt to it.

As iI mentioned in my last message, iI left my previous job and recently started a new one.

"I" is always capitalized

It's been almost a week since i joinstarted, and i'I am really enjoying it.

You mentioned your job so far, which you have "started." You could alternatively mention your company to say "... since I joined the company..."

I' am currently ingoing through the onboarding proccess, and iI've been noticed a few things about it.

"I am" can be contracted to "I'm," but there is no apostrophe when saying "I am."

The biggest change is iI feel is the sense of freedom, i mean there is a from the flexible working hours in, which is a contratst to my previous job has a's strict working horurs.

More natural

I also have more home office opportunities, it. It's a litibtle bit strange, but iI have to fitadapt to this situtation.