In order to get all fields of an Object in Salesforce, getGlobalDescribe() and getDescribe() from the Schema class can be utilized or we can query the FieldDefinition entity.

Sample Code:

public String obj = 'Account';
Map < String , Schema.SObjectType > globalDescription = Schema.getGlobalDescribe();
Schema.sObjectType objType = globalDescription.get(
	obj
); 
Schema.DescribeSObjectResult objectResult = objType.getDescribe(); 
Map < String , Schema.SObjectField > mapFieldList = objectResult.fields.getMap();  

for ( Schema.SObjectField field : mapFieldList.values() ) {  

	Schema.DescribeFieldResult fieldResult = field.getDescribe();
	
	if(fieldResult.isAccessible()) {  
	
		System.debug(
			'Field Name is ' + 
			fieldResult.getName()
		);
		
	}  
	
}

Sample Code:

EntityDefinition objED = [
    
    SELECT DurableId
    FROM EntityDefinition
    WHERE DeveloperName = 'Account'
    
];
List < FieldDefinition > listFieldDefinitions = [
    
    SELECT QualifiedAPIName
    FROM FieldDefinition
    WHERE EntityDefinitionId =: objED.DurableId
    
];

for ( FieldDefinition objFD : listFieldDefinitions ) {

    System.debug(
        'Field Name is ' +
        objFD.QualifiedAPIName
    );

}