Buy the soldered RAM upfront.

Yes. Paying for higher RAM when you order the laptop is almost always cheaper than trying to upgrade later.

Soldered RAM means nothing is upgradeable. So you have to buy exactly what you need at purchase time. And the premium manufacturers charge for a RAM bump is usually less than what you’d spend on a whole new machine or a third-party upgrade service later (if one even exists). Apple, Dell, Lenovo all price the RAM upgrade at something like $200 for a $30 part. But that $200 hurts less than realizing you’re stuck with 8GB two years from now and having to sell the laptop at a loss to buy a 16GB version.

The only exception: if you’re sure you can upgrade yourself with standard SODIMM slots. But those are getting rare. If the RAM is soldered, just pay the upcharge. Future You will thank you.

Don’t try to save a hundred bucks now and regret it for the next four years.