# disable the file picker
driver.execute_script("""
    HTMLInputElement.prototype.click = function () {
        if (this.type !== 'file') {
            HTMLElement.prototype.click.call(this);
        }
        else if (!this.parentNode) {
            this.style.display = 'none';
            this.ownerDocument.documentElement.appendChild(this);
            this.addEventListener('change', () => this.remove());
        }
    }
    """)

# perform the click
driver.find_element_by_xpath('//button[normalize-space()="Upload"]')\
    .click()

# assign the file to the <input type="file">
driver.find_element_by_css_selector('input[type=file]')\
    .send_keys(r'c:/myimage.png')