For people that still don't know how to get there, go in the settings on your TWITCH launcher, there is a tab called Minecraft, I was confused on this and figured somebody else was so here.https://gyazo.com/ffc3b36959ce1ca81df6c9a5c43a3c1b
2 years on, and this post saved me from a lot of frustration. Thank you!
For anyone like me on the updated twitch launcher.
-Click the mods tab at the top
-choose sky factory 4 ( double click skyfactory icon)
once that pops up
-click the settings gear (Next The subscribe button)
-choose profile options
-then uncheck “use system memory settings” and adjust to ur hearts content