Access Denied error while getting checked out file without any version for read only site in SharePoint online environment

I am using the following CSOM code to get the checked out files without any version

using (context)
            {
                List list = context.Web.Lists.GetById(new Guid("List id as string"));
                
                 var  checkedOutFiles = list.GetCheckedOutFiles();
                 context.Load(checkedOutFiles, c => c.Include(i => i.CheckedOutBy, i => 
                 i.ServerRelativePath));
                  try
                {
                    context.ExecuteQuery(); ;
                }
                catch (Exception ex)
                {
                  // exception in case of read only site collections: Access denied
                   // working fine for others 
                }
               
}

It is working fine for all libraries in all subsites in site collections which have isReadOnly=false,
But in case IsReadOnly=true , I am getting an access denied error.

For those site collections in "IsReadOnly"= true , I am having no trouble reading properties for a site,subsite, groups, permissions,user,items etc.

My ACS token has full control app only permission to all the site collections in the tenant