Hi,
Per Google requirements, notification "appearance" settings are now in Phone Settings, provided by Android. This applies to Android 8.0 and newer and Aqua Mail 1.18 and newer.
It's the same in all or nearly all apps (definitely Gmail, Twitter, others which had recent updates).
Phone Settings have options for sound, vibration on/off.
There is no option for LED color (Google forgot, manufacturers don't seem to care).
There is no option for vibration pattern.
Some phones don't have an option for LED on/off. Some phones don't have an option to choose a particular sound, only on/off, using the "global" notification sound setting (which can be changed, but will affect all modern apps).
On some phones the LED will only flash if there is a sound or vibration (doesn't make sense to me, but this is Google). Some phones have a well hidden setting to "pulse the LED", some do not.
All this mess is completely out of our control. Notification appearance settings are now provided by Android (and can vary from device to device) and cannot be overridden by apps.
Google is strong-arming developers into this, it's not optional (if an app does not opt into the new scheme - it's not possible to release updates to Play since November 1, 2018... and we do want to).
If your phone is missing some options (e.g. a way to choose a sound) or some of them don't work - please contact your phone manufacturer's support and let them know. Them and Google are the only ones who can fix this.
How interested they are is another matter, but there is hope since this affects all apps now, and your phone manufacturer can fix this in "their" Android "flavor" without waiting for Google's next Android update.