Try to use SAVE instead of UPDATE…
import wixData from 'wix-data';
$w.onReady(()=>{
$w('#btnSave').onClick(()=>{
let toSave = {
"projectName": $w('#iptProjectName').value,
"projectDescription": $w('#iptProjectDescription').value,
"projectDetail": $w('#iptProjectDetail').value,
"projectCategory": $w('#iptProjectCategory').value
};
wixData.save("Projects2", toSave)
.then( (results) => {
let item = results;
})
.catch( (err) => {
let errorMsg = err;
});
wixWindow.lightbox.close();
});
});