Hi, I do not see any built-in option, but I believe you should be able to achieve it by writing some JavaScript to automatically trigger the save at an interval or a detected change.

In the form that you want the auto save , 

You can place the custom HTML and add this code . 
Adjust accordingly :  

<script>

$(document).ready(function () {
    function autosaveForm() {
        var formData = $('#formId').serialize(); // Replace 'formId' with your actual form ID
        
        $.ajax({
            type: 'POST',
            url: '/web/json/workflow/form/save', // Replace with your actual endpoint
            data: formData,
            success: function(response) {
                console.log('Form autosaved successfully:', response);
            },
            error: function(xhr, status, error) {
                console.log('Autosave error:', status, error);
            }
        });
    }

    // Set interval to autosave form every 30 seconds (30000 milliseconds)
    setInterval(autosaveForm, 30000);
});

</script>

On the other hand, You might be able to leverage the multi page form element to segregate the long forms to different sections. 

This Feature has the ability to auto save content even without clicking the submit button.
Multi Paged Form#,Data%20Storing,-Name