Yes, the OEM typically defines it as have X amount of Slots, and will also advise options on how to fill it, or will tell you how they offer it.
For example an LG Laptop I randomly found on the Web says => "16GB DDR4 3200MHz - 8GB x 1 (On Board) - 8GB x 1" => which means this one has hard wired non-removable 8 GB Ram Stick and one in a removable slot. Some cheaper versions will only offer it with the 8 GB hard wired chip, and advise 1 Slot empty for future expansion.
Sometimes, a vendor isn't forthcoming with the details, and you may have to ask them, the OEM, or another supplier for the info. For example Costco.com. I randomly picked an inexpensive
HP 14" Laptop - 11th Gen Intel Core i3-1125G4 - 1080p Windows 11 - Model 14-dq2053cl => $499 (no Black Friday Special yet). In their specifications it just says 8 GB and no designation if it's 4+4 in 2 slots or 8GB in a single slot.
So a quick Google search with "hp 14-dq2053cl specs" and a link to HP Support pops up. It advises Standard Memory is:
8 GB DDR4-3200 MHz RAM (1 x 8 GB) => Which means it's a single Ram chip.
Then another quick Google search with "14-dq2053cl ram upgrade" and a link to Crucial (a memory manufacturer) pops up. It says for the model requested:
Maximum memory:
16GB
Slots:
2 (2 banks of 1)
Standard memory:
8GB removable
So that tells you there's room for expansion as it comes with one slot filled with 8 GB.
Like I said earlier, if you find something of interest to you, just post the link and some us will review and advise if we think it's a good fit.
Happy Shopping.