The cutoff will be released in first week of january. The merit list will be prepared on basis of these cutoff marks. The cutoff may slightly vary from year to year. You can check the relevant data from this article https://school.careers360.com/articles/ntse-karnataka-cutoff .
Hope this helps.
The cut off for NTSE 2020 stage 1 for Karnataka state category wise is as follows
General category 143
SC category 119
ST category 104
The determining factors which decides the cut off are number of candidates appeared, difficulty of exam, highest and lowest marks. Cut will be declared along the results. As cut off changes every year it may increase or decrease slightly.