We have 50,000 distinct product IDs. What versions of Quickbooks are able to support up to 100,000 products, syncing from Vend or Finale Inventory?

There is no item limit in QBO.

https://quickbooks.intuit.com/learn-support/en-au/other-questions/quickbooks-online-file-size-and-fe...

But you have to use QBO Plus or Advanced to manage inventory item.

https://quickbooks.grsm.io/US

https://quickbooks.grsm.io/us-promo

Should you prefer QB Desktop, you have to use Enterprise edition to manage up to 100K inventory item and more.

I notice FI supports both QBO and QBD. Should you need comparing to other inventory management apps, explore these options

http://www.primaseller.com/?utm_source=Affiliate&fp_ref=primaseller

https://go.tradegecko.com/register?code=fiat-lux

https://www.zaperp.com/ref/25/