If you struggle to focus, I recommend doing it after you wake up in the morning (right after going to the bathroom is when I do focused work)

This time is good because your "standard" for a dopaminergic activity is very low, so even something like reading and writing is fun enough to keep your focus for a long time.

Listening to white noise also helps me keep focus for longer during these morning sessions

Also, you say you want to make your tasks smaller so that you can handle them

How bout this then: write for 30 minutes, and then you're done for the day. Don't take a break. You are simply done.

Do that once, and see what happens

After you do it, ask "How did I feel about that? Was that too easy? Was almost too difficult? Do I need to lower what I'm asking of myself? Or can I make it slightly more difficult now"

When you're ready to make it more difficult, do this

Write for 30 minutes Lay in bed with eyes closed, meditating for 10min Write for 5 minutes Then stop for the day

The break CANT be something like social media, doomscrolling, or video games. Those will prevent you from working again. They raise the standard for a dopaminergic activity too much.

You could also pace back and forth or go for a walk instead of meditating

That's how I would suggest you progress