Works for me with J! 4.0.2. Well, I've only tried it with the field type of radio not list.

Does it work if you remove the multiple="true"? I'm not sure it's supposed to work with multiple.

Joomla 4: It works when the list is single selection (no multiple=true), it does not work with multiple=true.
Joomla 3: Works for both

@Fedik @dgrammatiko Did any of you change the showon JS code for J4? Could that be the issue here?

Did any of you change the showon JS code for J4?

Yes, the showon is completely rewritten in J4 as vanilla JS (no jQuery) but I think the problem comes from the field, eg probably the choices.js part or the parent Custom Element. The first one I wrote the code for the other was @Fedik (I think, might be wrong)

@boddunan does it work if remove layout attribute? when use generic <select>

No, removing the layout attribute shows a multi-select list box. Selecting options does not show other fields.

thanks for checking,
so it seems the bug in shwoon js, need to look how it handle multiple values

If someone can test replacing this

            // If checkbox or radio box the value is read from properties
            if (originField.getAttribute('type') && ['checkbox', 'radio'].includes(originField.getAttribute('type').toLowerCase())) {
              if (!originField.checked) {
                // Unchecked fields will return a blank and so always match
                // a != condition so we skip them
                return;
              }

              itemval = document.getElementById(originId).value;
            } else if (originField.nodeName === 'SELECT' && originField.multiple) {
              itemval = Array.from(originField.querySelectorAll('option:checked')).map(el => el.value);
            } else {
              // Select lists, text-area etc. Note that multiple-select list returns
              // an Array here s0 we can always treat 'itemval' as an array
              itemval = document.getElementById(originId).value;
              // A multi-select <select> $field  will return null when no elements are
              // selected so we need to define itemval accordingly
              if (itemval === null && originField.tagName.toLowerCase() === 'select') {
                itemval = [];
              }
            }

The solution should be either that or something similar (I can't test this atm)

that will not work, there no field type="select" ?
should be element.nodeName === 'SELECT'

Hello,
Today I came across the same problem. Showon in Joomla 4 doesn't work for field list when it has 'multiple' attribute (as mentioned before) and also doesn't work for field of type 'checkboxes'.

Same issue here.

I almost submitted a new issue! I wrote this description:

Steps to reproduce the issue

1. Check the banners config.xml: www/administrator/components/com_banners/config.xml
2. The config has the fields save_history (radio) and history_limit (number) showon="save_history:1"
3. When you go to the config form, you can enable "Enable Versions" and it shows the "Maximum Versions" associated field
4. Change the save_history (radio) to save_history (list), type="list", it still works OK
5. Remove the layout to save_history (list), layout="joomla.form.field.radio.switcher", it still works OK
6. Add the multiple="true" to the save_history (list), the shown conditional field doesn't work.

		<field
			name="save_history"
			type="list"
			label="JGLOBAL_SAVE_HISTORY_OPTIONS_LABEL"
			default="0"
			multiple="true"
			>
			<option value="0">JNO</option>
			<option value="1">JYES</option>
		</field>

Expected result

The shownon behaviour must support the multiple attribute (as it worked before on Joomla 3)

Actual result

The shownon behaviour doesn't support the multiple attribute.

@anibalsanchez can you test #35486 (comment)

Please test #35723

@dgrammatiko The comment was almost there. I was writing about the array name just when you submitted the PR. ;-)

closing as we have a pr #35723