There are some DIY type notebook in the market, like the Framework one, that user can replace individual h/w parts. I just wonder if there's a standard design of notebook of the same class that uses compatible h/w, such as display, wireless, power...etc., so that user can install different mother board on it. For example the Pinebook Pro, if the display in use is a common type, user can replace the m/b with a more powerful one, such as the new Pi 5. I don't know if there's any 'barebone' notebook available that user can customize with different m/b and add-ons of choice ?

Short Answer - NO!

Notebooks wrap the components inside the case, and measurements have to be exact. Far too many things are unique to each notebook model, never mind each manufacturer.

Do what I did - buy a pc if you want to swap parts. You don't ever have to buy another, as you can keep replacing stuff - even the case!

In my experience, the design of notebook computers simply does not allow for any "field-replaceable parts."

There are a few DIY laptops like the Framework where you can replace parts but as posted there isn't a standard specification like the desktop ATX (as far as I know) where you can install generic parts.

Correct. There's also huge issues in the way. For instance, a cpu & heat sink have to be squeezed between case & keyboard, with clear paths from air inlets and nothing heat sensitive on the path out. The design of the pcb has to be finely tuned to minimise capacitance, cross-talk, etc. <snip boring detail>. That very definitely affects component locations. In short, designing a laptop can be compared to building a ship in a bottle.

Now you're coming along, wanting to change the poop deck and add an extra mast.....

Thank guys for the reply. One day I tried to fix 2 notebook with power on/battery problems, one was a Samsung and the other was a Lenovo Ideapad. I was surprised to see they looked almost the same inside, I believe Samsung was the OEM. So I think that kind of mass produced entry level units were using the same display, power supply, battery...etc. that we could use with other motherboards and SBC. There are tons of Pi DIY projects with LCD, I don't know if there's standard interface on LCD, or compatible to the CSI i/f on the Pi, so that I could install a Pi CM4 for example to replace the m/b on a faulty notebook, that can produce a normal size thin notebook instead of using the Pi 4 SBC. Similarly, I could do the same to the Pinebook Pro and Pinetab 2 for example, which have plenty of space inside the chassis I can make good use of, such as to install a more powerful SBC, as long as the LCD is compatible that’s the main concern.