I have a room I work in - you don't have this luxury, if I didn't I'd dedicate a space to the same purpose, even one end of a table or a corner of the living room. When my working period starts I dress for the office (not completely, I wear shorts and a T-shirt but due to Zoom meetings etc I clean up because I will be on camera) and when I go into that space, that's where I work, procrastination and fecklessness aside.

Conversely, when I leave that space I am no longer working, pages aside. I do check in on email via phone if there are things that need to be checked on, but otherwise I try very hard to leave my work in that place.

I think the ritual is almost as important as the place, both for "clocking in" and "clocking out". Even if it's just open/closing a laptop or turning a monitor on/off, it's training yourself to see that as the gate for being "on" and being "off".

If your work laptop is your personal laptop, you might also need to have two accounts and sign out of your work account/into your personal account at the end of the day for Ycombinator time, personal use, etc.