When adding a collapse div (bootstrap 5) then it is not possible to edit collapsed content.

<div id="collapse-3" class="card-collapse collapse">
Test
</div>

Removing class collapse shows content.

Any workaround in editor? Like "show hidden elements" function or so that I am missing?

Didn't work. The style does not affect the collapse even though i added a custom stylesheet as last stylesheet both in admin template and in frontend template and also in JCE custom style template global configuration.

.mceContentBody .collapse, .mceContentBody .collapse:not(.show) {
display: inherit !important;
}

does nothing and when inspecting element with class collapse in backend then

.collapse:not(.show) {
display: none;
}

from

administrator/index.php?option=com_jce&task=editor.pack&type=css&slot=content& ...(hash code or something that i removed)... =1&context=22&profile_id=5

is loaded and hides the div.

So issue was the compress CSS setting. Changed it to no and it solved the issue!

Thanks and have a good weekend!