I have been looking up information on how to manage playing modded Minecraft for 1.12 on a weaker computer and discovered the concept of portable Minecraft. Years ago there was an app that would transfer your data onto a flash drive and boom, Minecraft that shouldn't drain your computer and instead relies on the RAM of the flash drive instead. Ever since 1.10 however the app had ceased updating but a new method came along where one could directly format a flash drive to do what you want it to do.
Now I followed this guide on this site here (the article is dated 2017, just around the time when 1.12 was released give or take, though it may have been published a while before 1.12 even existed, im not sure) following the directions to the letter from copying files and transferring the game launcher to a custom-made bin file, and all. Yet when I run the game, it still massively drains my computer like it did before. I dunno if it is due to the flash drive itself being insufficient (which it shouldn't even if it isn't the best for the job) or if I have a setting or two on the launcher itself wrong. I followed every step correctly in the above article so I know that I didn't skip a step.
My computer has 4 gigs RAM and the flash drive itself is 16 gigs (specifically a 16 gigabyte SansDisk, one of the recommended models by said article). My processor and graphics card are capable of supporting Minecraft relatively fine, RAM is my only main issue which is why I began looking up this possible fix at least until I am able to buy some RAM sticks to install into my computer. If the guide I used is not compatible with 1.12.2, I hope someone can suggest a different means to achieve the same goal using a flash drive.