The start method queries for all accounts that have multiple opportunities, and the execute method deletes all but the latest opportunity for each account. The query used in the start method retrieves the Account records along with their Opportunities subquery, sorted by CloseDate in ascending order. We then use the opportunities.sort method to sort the opportunities list in ascending order by CloseDate, and use the opportunitiesToDelete.addAll method to add all but the latest opportunity to a list of opportunities to delete. Finally, we use the delete statement to delete all opportunities in the opportunitiesToDelete list.
Try the code :

global class DeleteDuplicateOpportunities implements Database.Batchable<SObject> {
    
    global Database.QueryLocator start(Database.BatchableContext context) {
        // Query for all accounts that have multiple opportunities
        String query = 'SELECT Id, (SELECT Id, CloseDate FROM Opportunities ORDER BY CloseDate DESC LIMIT 1 OFFSET 1) FROM Account WHERE Id IN (SELECT AccountId FROM Opportunity GROUP BY AccountId HAVING COUNT(Id) > 1)';
        return Database.getQueryLocator(query);
    }
    
    global void execute(Database.BatchableContext context, List<Account> scope) {
        List<Opportunity> opportunitiesToDelete = new List<Opportunity>();
        for (Account acc : scope) {
            List<Opportunity> opportunities = acc.Opportunities;
            opportunities.sort((a, b) => a.CloseDate.compareTo(b.CloseDate));
            opportunitiesToDelete.addAll(opportunities.subList(0, opportunities.size() - 1));
        }
        delete opportunitiesToDelete;
    }
    
    global void finish(Database.BatchableContext context) {
        // Optional: add post-batch processing logic here
    }
}