Doubt what you seek exists. Never heard of any "stand alone monitor/keyboard" with that kind of hardware/technical capability. However you can use a utility like TeamViewer to remotely control a desktop from a laptop and accomplish your objective. Simple. Easy. Works well. https://www.teamviewer.com/en/
I just built an mini-ITX desktop (Cooler Master Elite 110), it's small enough not to be an eyesore and big enough to handle most full sized components (it has problems with graphics cards bigger than 22cm but you still have plenty of choice within that limitation). Performance components tend to be heavier, therefore it's not something you want to carry in your hand but it would fit perfectly in a car, therefore it is "portable".
I have a Microsoft Surface 2nd gen and I do believe it's a perfect 'portable' replacement for a desktop. You can find the 1st and 2nd gen at a fairly cheap price SH of course and it gets the job done with the intel i core and 4 GB of RAM. If you also buy a docking station like this then you are all set imo, many ports - including Ethernet - and much less pounds than a desktop system or the All-In-One. Of course, you can also try the cheaper Windows tablets like ASUS Transformer T100 with docking keyboard or the 10-inch Lenovo Miix 3 with folio keyboard included but bear in mind that these two tablets won't be able to stand much heat tasking-wise
But it's really that small boxes in suitecase which are the solution which you are looking for really, simply do believe me and that's it. There is no other way about it for example. How do you plan to go around ? It costs in new case for now like 100 dollars and above.
This is perhaps best called a “thin client” laptop. Aka a “diskless client,” or for politically incorrect, a “dumb terminal.” Typically a desktop monitor, keyboard, and mouse that boots from the network server. You stumped me on this one! I can’t find a thin client with a laptop form factor! Perhaps buy a Chromebook with a nice display, and configure it to boot from your server. Check these links: https://linustechtips.com/main/topic/808189-desktop-and-diskless-laptop/