I know fetching multiple ids has been possible for some time and it work in my implementation:

GET /crm/v4/Deals?ids=123,456,789&fields=Deal_Name,Stage,Account_Name

...but it's not documented anywhere in https://www.zoho.com/crm/developer/docs/api/v4/get-records.html

This post is almost a duplicate of a previous issue raised 10 years ago, hence I am opening this new one for visibility reasons. See https://help.zoho.com/portal/en/community/topic/is-there-any-way-to-retrieve-multiple-records-by-providing-their-record-ids