triggerable property from the object schema can be used to determine whether Trigger can be developed on that object.

Sample Code(Trigger not allowed):

Map < String, Schema.SObjectType > globalDescription = Schema.getGlobalDescribe();
Schema.SObjectType sObj = globalDescription.get( 
    'ConversationEntry' 
);
Schema.DescribeSObjectResult sobjDesc = sObj.getDescribe();
String sObjStruct = JSON.serialize( 
    sobjDesc 
);
System.debug( 
    'sObjStruct is ' + 
    sObjStruct 
);
JSONParser parser = JSON.createParser( 
    sObjStruct 
);

while ( parser.nextToken() != null ) {
    
    if (
        parser.getCurrentToken() == JSONToken.FIELD_NAME &&
        parser.getText() == 'triggerable'
    ) {
        
        parser.nextToken();
        System.debug(
            'triggerable is ' + 
			parser.getBooleanValue()
		);
        break;

    }

}

Output:

Sample Code for Account Object(Trigger is allowed):

Map < String, Schema.SObjectType > globalDescription = Schema.getGlobalDescribe();
Schema.SObjectType sObj = globalDescription.get( 
    'Account' 
);
Schema.DescribeSObjectResult sobjDesc = sObj.getDescribe();
String sObjStruct = JSON.serialize( 
    sobjDesc 
);
System.debug( 
    'sObjStruct is ' + 
    sObjStruct 
);
JSONParser parser = JSON.createParser( 
    sObjStruct 
);

while ( parser.nextToken() != null ) {
    
    if (
        parser.getCurrentToken() == JSONToken.FIELD_NAME &&
        parser.getText() == 'triggerable'
    ) {
        
        parser.nextToken();
        System.debug(
            'triggerable is ' + 
			parser.getBooleanValue()
		);
        break;

    }

}

Output:

Using this sample apex code snippet, we can find whether the object supports trigger or not.