Did you logout and log back in after installing the package? If not please do so.
If that doesn't help too, please create a new external account and see if AEM is listed under Type
From your screenshot it appears that you have installed every available package on your sandbox instance. Hope you have the license for all of them.
I'll suggest you to do the following
2. Logout and log back in to see if this helps.
3. if not, execute postupgrade -force from backend.
4. If that also doesn't help, make a fresh install and this time add the required packages only. Especially avoid Leads and Mid-sourcing packages.
Thanks. I tried the steps mentioned above but still can not see "AEM" listed in Type. I also did fresh installation with only AEM integration selected but the situation still the same.
I checked the logs generated during the installation, following is the snippet where i can't see any entities being saved in nms:extAccount.
Line 211: 11:10:41 - Package 'AEM integration': Saving entities of type 'xtk:group'...
Line 212: 11:10:41 - Package 'AEM integration': Saving entities of type 'xtk:operator'...
Line 213: 11:10:41 - Package 'AEM integration': Saving entities of type 'xtk:rights'...
Line 214: 11:10:41 - Package 'AEM integration': Saving entities of type 'nms:seedMember'...
Please advise if I am missing something.
Also try importing this package to your instance
<package author="Internal account" buildDate="2018-08-09 06:39:50.612Z" buildNumber="8896"
<extAccount account="campaign-remote" activationMode="1" label="AEM instance"
name="aemInstance" server="http://localhost:4502" type="12">
<folder _operation="none" name="nmsExtAccount"/>
Is this issue part of particular build number? if yes, please advise how can i fix this.