Having a similar issue where my Feed The Beast launcher will not even open. I have done the usual reinstall Java/Minecraft/FTB launcher and have had no luck.
When I run java -version, I get
"
java version "1.8.0_231"
Java(TM) SE Runtime Environment (build 1.8.0_231-b11)
Java HotSpot(TM) 64-Bit...