Sumbit or Post file, image from Ajax JQuery + PHP it’s very simple code.

Form HTML :

<div class="col-3 ml-3">
<h4>Register</h4>
<form id="sigup">
<div class="mb-3">
<label for="exampleInputEmail1" class="form-label">Name</label>
<input type="email" class="form-control" name="name">
</div>
<div class="mb-3">
<label for="exampleInputEmail1" class="form-label">Profil</label>
<input type="file" class="form-control" id="profil" name="profil">
</div>
<div class="mb-3">
<label for="exampleInputEmail1" class="form-label">Username</label>
<input type="text" class="form-control" name="username">
<div id="emailHelp" class="form-text">We'll never share your username anyone!</div>
</div>
<div class="mb-3">
<label for="exampleInputPassword1" class="form-label">Password</label>
<input type="password" class="form-control" name="password">
</div>
<p id="msg"></p>
<button id="redirect" type="button" class="btn btn-primary">Sig Up</button>
</form>
</div>

Ajax Jquery

<script type="text/javascript">

$(document).ready(function(){ 
$("#redirect").click(function(){

var formData = new FormData($('#sigup')[0]);
console.log(Object.fromEntries(formData));

$.ajax({
type: "POST",
url: "<?=base_url('user/reg');?>", 
//data:JSON.stringify(Object.fromEntries(formData)),
data:formData,
//contentType: "application/json", 
contentType:false,
processData: false,

success: function(res){
if(res==1){
msg_('<font color=green> Add succesfully.</font>');
$('#sigup')[0].reset(); 
console.log(res); 
// storing url and time 
$("#redirect").text("Redirecting.."); 
let delay =5000; 
let url = "<?= base_url('/cart');?>"; 
setTimeout(function(){ 
location = url; 
},delay); 
}else{
msg_('<font color=red>'+res+'</font>');
console.log(res); 
} 
},

error: function(res){ // respon ajax, jquery before controller 
console.log(res);
}
});// you have missed this bracket

});
});


</script>

Note : reqired setup!

contentType:false,
processData: false,

Get respon value data PHP file, image:

<?php

// get data file
$namaFile = $_FILES['profil']['name'];
$namaSementara = $_FILES['profil']['tmp_name'];

// folder file images
$dirUpload = "media/";

// send file
$terupload = move_uploaded_file($namaSementara, $dirUpload.$namaFile);

if ($terupload) {
echo "Upload successfuly.<br/>";
echo "Link: <a href='".$dirUpload.$namaFile."'>".$namaFile."</a>";
} else {
echo "Upload failur!";
}

?>