Q.Sick flower leaves
I’ve germinated some local commercial dahlia and zinnia seeds.2 weeks later planted then in small pots using local nursery garden soil. After a while the upper leaves turned curly and the growth appear stunted. Does anyone have any idea what causing it? Disease from the soil, pest or plant overheat because i’m living here in malaysia. Thank you

There may be more than one thing causing these signs of disorder. I live in Thailand and with the current wet season it is hard to keep plants pest and disease free.
The dried discolored drying/dying growth could be from a fungal disease. And the new leaf distorted growth is probably a sucking insect pest on the under side of the leaves, like aphids or psyllids or leaf hoppers. And sometimes it is the pest that vectors/introduces the pathogen into the plant tissue.
All you can do is to keep the plants as healthy as possible with good water management and fertilization.
I don't know your resources there in Malaysia, but here in Thailand the large shops like TESCO and HOMEPRO have some gardening proucts, and we have Lazada. I see that Lazada is in Malaysia too, and they have a neem oil product available that can be used for pest suppression. You will need a small spray bottle. https://www.lazada.com.my/products/organic-verdana-cold-pressed-neem-oil-32-fluid-ounce-un-refined-filtered-high-azadirachtin-content-for-indoor-and-outdoor-plant-spray-plant-care-pet-care-skin-care-hair-care-i145050411-s169008783.html?spm=a2o4k.searchlist.list.19.356a5027Q68uel&search=1
This Black Gold organic fertilizer product looks good,but I haven't use it. It has a trichoderma biological fungicide component too. This can be sprayed and applied as a soil drench.
https://www.lazada.com.my/products/blackgold-bio-organic-fertilizer-with-trichopower-mix-greenearth-re-packing-1-kg-i360566918-s511144644.html?spm=a2o4k.searchlist.list.5.513e7cd5EwuDOD&search=1