Do you need it to be impossible to choose? Then use HTML Input file accept property. accept="image/png"
for instance.
Or you want it to filter from the input after the user selected it?
Then you should use a custom directive or check for the file types in the ts code upon upload.
EDIT
in that case, in your code:
onFileChange(event) {
const fileList = event.target.files;
console.log("User selected fileList:", fileList)
Array.from(fileList).filter(
item => {
console.log("file mime type:", item['type'])
})
const filesToUpload = Array.from(fileList).filter(
item => { return item['type'] != "application/zip" })
console.log("reduced list:", filesToUpload)
}
Working stackblitz example here.