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.
CO-wash: Inecto coconut
Treatments: Komaza Matani, coconut oil, Hairveda Sitrinillah
Leave in: Fructis Sleek & Shine (old), Gliss ultimate volume, Inecto argan
Styler: Umberto Giannini jelly, Boots Essentials gel
Experimenting with: going back to basics