How many books allowed in iBooks macOS app ?

Hi dear Apple Community!

How many books (both PDF, .ePub, etc formats) allowed to put in Apple Books (former iBooks) macOS Catalina app ?

(Of course I have largest iCloud storage plan 2Tb available on fall 2020)

The question come from decision to put all books collected during the last 20 years (non-fiction, previous purchase from Amazon, previous purchase from private publishers, technical user/service manuals, etc...) to the Apple ecosystem.

Due iBooks still not is not so good in UI/UX (and an addition have pure books catalogs organizing) I try to find something better, but developer stop working on a really great iDocument Plus macOS app, and after 64bit Catalina come, iDocument Plus just unable to start...

Many thanks to all Your opinion!