How to find elements in containers that open when buttons are pressed - python-3.x

Question

I am using headless Firefox on Selenium and XPath Helper to identify insanely long paths to elements.
When the page initially loads, I can use XPath Helper to find the xpath of any element of interest, and selenium can find the element when given the xpath.
However, several buttons that I need to interact with on the page open menus when pressed that are either small or take up the whole "screen". No matter their size, these containers are overlaid on the original page, and although I can find their xpaths using XPath Helper, when I try to use those xpaths to find the elements using selenium, they can't be found.
I've checked, and there's no iframe funny business happening. I'm a bit stumped as to what could be happening. My guess is that the page's source code is being dynamically changed after I press the buttons that open the menu containers and when I call find_element_by_xpath on new elements in the containers, the original source is being searched, instead of the new source. Could that be it?
Any other ideas?
As a workaround, I can get around this issue by sending keystrokes to the body of the page, but I feel this solution is rather brittle and likely to fail. Would be a much more robust solution to actually specify all elements.
EDIT:
With selenium I can find the export button, but not the menu it opens.
Here is the code for the export button itself:
The element of interest for me is "Customize Export" which I have not been able to find using selenium. Here is the code for this element:
Notice the very top line of this last image (cdk-overlay-container)
Now, when I refresh the page and do NOT click the export button, the cdk-overlay-container section of the code is empty:
This suggests my that my hypothesis is correct -- that when the page loads initially, the "Customize Export" button is nowhere in the source code, but appears only after "Export" is clicked, and that selenium is using the original source code only --not the dynamically generated code that appears after clicking "Export" -- to find elements

Answer 1

Selenium could find the dynamic content after doing
driver.execute_script("return document.body.innerHTML")

Answer 2

The WebDriverWait is what you need to use to wait for a certain condition of elements. Here is an example of waiting for the elements to be clickable before the click with a timeout in 5 seconds:
wait = WebDriverWait(driver, 5)
button = wait.until(EC.element_to_be_clickable((By.XPATH, 'button xpath')))
button.click()
wait.until(EC.element_to_be_clickable((By.XPATH, 'menu xpath'))).click()
identify insanely long paths
is an anti pattern. You can try to not use XPath Helper and find xpath or selector yourself.
Update:
wait = WebDriverWait(driver, 10)
export_buttons = wait.until(EC. presence_of_all_elements_located((By.XPATH, '//button[contains(#class, "mat-menu-trigger") and contains(.="Export")]')))
print("Export button count: ", len(export_buttons))
export_button = wait.until(EC.element_to_be_clickable((By.XPATH, '//button[contains(#class, "mat-menu-trigger") and contains(.="Export")]')))
export_button.click()
cus_export_buttons = wait.until(EC. presence_of_all_elements_located((By.XPATH, '//button[contains(#class, "mat-menu-item") and contains(.="Customize Export")]')))
print("Customize Export button count: ", len(cus_export_buttons))