Navigation dropdown menus with submenus should have a submenu indicator.

In MkDocs 1.5.2 this looks like the following:

However, this indicator is invisible in MkDocs 1.6.1:

It does appear when you hover over it however, so it's just a styling issue:

Workaround

Looking at a wiki produced with MkDocs 1.5.2, the following CSS was defined:

.dropdown-submenu > a::after {
	border-left-color: #ccc;
}

In 1.6.1, this changed to:

.dropdown-submenu > a::after {
	border-left-color: var(--bs-dropdown-link-active-color);
}

var(--bs-dropdown-link-active-color) appears to be defined as #fff rather than #ccc, which is why the marker is no longer visible. (White marker on white background.)

A quick workaround is to copy the old .dropdown-submenu > a::after definition above into your custom CSS.

Another option is to use var(--bs-dropdown-link-color) (rather than --bs-dropdown-link-active-color), however, this results in a darker coloured marker than in MkDocs 1.5.2.

Edit: This appears to be the relevant code:

And here's the commit in question:
351b879#diff-3c532a99d2626b4b3913ddf86623f6dc6593ef2da6c3e1e4b8407cbf41dd2cb9L277