Yes highlighting and heat styling can damage the curl pattern, temporarily or permanently. Work with your hair properties, if your hair is fine or damaged use hydrolysed protein, if it's porous or lacking in elasticity use coconut oil. Also beneficial for damaged hair includes ceramides, 18-MEA and panthenol.
I find my underlayers suffer from drying out too quickly when plopping too.
2a-2c, medium texture, porous/ colour treated. Three years CG, growing out mechanical and chemical damage = breakage and very high porosity. Past armpit length heading for waist.
Treatments: Komaza protein, Komaza Matani, coconut oil with sugar syrup. Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume
Styler: Umberto Giannini jelly, Boots curl creme, Rockin RInglets
Experimenting with: Mega-Tek, Curl Harmony reviver, Elvive Full Restore 5.