If you complete this task easily and effortlessly, you can use a reliable software like Softaken OST to PST Converter Software. This professional solution allows you to convert OST files while keeping the email, contacts, calendars, and other mailbox data in PST format. It is designed to keep the original email formatting and structure during the conversion. It offers a selective conversion feature that allows you to convert only the desired data that you need to convert. This software works fully independently; MS Outlook or any other application is not required. Its simple interface allows you to operate it without having any technical expertise. Moreover, this advanced application is designed to run smoothly on all the latest and oldest Windows OS versions.

You can split a large ICS file by exporting each event into its own ICS, and the easiest way is using SysTools ICS Splitter. It automatically breaks massive ICS files into smaller, event-based or date-based files while preserving all metadata, attachments, and formatting. The tool supports bulk processing, keeps the original folder structure intact, and avoids corruption issues common with manual methods. If you need clean, organized, shareable ICS files without hassle, this utility is a reliable, time-saving option.

I’ve faced the same issue; manually converting multiple ICS files is messy and risks losing recurring events or details. From my experience, SysTools ICS Converter is a solid choice for bulk conversion.

Why does it work well?

List item supports batch processing, add multiple ICS files or an entire folder at once.
Converts to PST, CSV, iCal/ICS, and other formats.
Preserves event details, including descriptions, attendees, and recurring events.
Can handle large ICS batches without errors.

Tips:
Always back up your original ICS files before conversion.
After conversion, spot-check a few events to ensure recurring events and reminders are intact.
If using CSV, check that all columns (start/end, description, attendees, etc.) are correct.
Overall, it’s a reliable way to quickly convert multiple ICS files without data loss, saving a ton of time compared to manual methods.