You might want to consider outputting to a specific format to make your processing of the file easier.
For example, a simple CSV format would probably suffice.
The data you are outputting should be fine - though you didn’t actually give any final file excerpt so there’s a bit of an assumption there.
Yes. The choice to go with notifications seems a bit counter-productive. As I said previously, a file based solution is almost certainly your best option.
That’s now a manually driven task to exfiltrate the information from the notifications.
If you want to use Shortcuts, then Dropbox is probably your best option. Assuming you haven’t succumbed to the Dropbox ninja issue, you should be able to write to a file via IFTTT and access the same file directly (without manual intervention), using the Get File action.
The text formatting I think would actually be text parsing in order to process the results. This is where the earlier choice of file format will pay dividends. You could use a simple Split Text action with a CSV, or if you were a little more creative with your file format and wrapped the contents with some additional text, you might even be able to transform the file into JSON for direct access to attributes. Depending upon how your are processing the file, this may be worth the additional effort.
I would recommend processing the file sequentially and considering some sort of approach of marking a status (e.g. write to a completed list then remove from the original), to allow you to recover from stalled processing.
Assuming you can build a Shortcut (including any additional ones that may be required as per your comment above) to do your processing, then I suspect that the IFTTT recipe and using Dropbox as the data storage medium will actually end up being one of the most straight forward aspects. It should just be a case of setting up a file structure and letting it run.
Hope that helps get things straightened out for you.