At this very moment my samples folder contains 3,953,005 objects (4 TB) only including audio and MIDI files / clips (no DAW project or library files, finished projects, mixdowns, stems, remix packs, acapellas, virtual instrument libraries, or music libraries included here).
Live 10 can handle it very well.
Indeed, what doesn't really work well is my favorite search function CMD+F, if I then enter a commonplace like "kick", "snare" or "crash", I may wait quite a while despite previous indexing. That's why I mainly work with the "Add Folder" function and add important subfolders to the sidebar as shortcuts. If these are selected, only the folder and its subfolders are searched, which works quite fast.
Here is another important hint that some Live users don't seem to notice. When searching via CMD-F, Live displays only files that can be used directly in Live (e.g. audio files, MIDI files, presets) but no folders and subfolders.
However, if you select a folder in the sidebar and then search directly via the search field (without CMD+F), the subfolder structure is also shown by Live, which is excellent. This has the enormous advantage that you get to the right areas very quickly, depending on the folder structure and its naming.
An example with respect to audio files, if I search for "house" via CMD+F, only audio files whose name contains "house" are displayed, e.g. "fat deep house kick.wav".
The advantage of searching with the pre-selected (added) folder is the following: If I select the folder "Loopmasters" in the sidebar, for example, and then enter "house" directly in the search above, I not only get audio files that contain the name "house", but also folders and subfolders that have the name in them! The trick is that I can now find a folder called "Fidget House", for example, and can open it immediately and find a substructure like Fidget House/Drum Hits/Kicks/FH_Kick_01.wav in it.
If I had searched through the general search, I would never have found the "FH_Kick_01.wav", because "house" is missing in the name itself. That's why I mainly search with pre-selected folders.
The overall trick is to simply name the top folder of a sample pack properly, that's enough! It's completely unnecessary to work with some special finders or third party apps - seriously how could I tag almost 4 million samples? The trick is simply to name the main folder explicit in the file itself - so this system can be used immediately in any DAW browser (which can search for files & folders).
For example, if a sample pack is only called "Division", I probably won't find it often enough sometime later, because the name is too abstract, so I will assign hashtags to the folder name myself when buying or adding it to my sample folder, after listening through it for a few minutes, the folder will be called "Division (#chillout #house #ambient)", done!
If I ever make ambient music now, all I have to do is search for "ambient" and I'll get the sample pack "Division" with all its subfolders where I can use the individual elements. The whole system works without having to tag every single sample. A hashtag is required at most for the main sample pack folder, if the name itself does not already include it (e.g. "Mega Super Deep House Drums", no tags needed at least for me).
Actually, I didn't want to write that much. What I really want to bring up as a feature request is what Cubase, Bitwig and Reaper can already do.
Use multiple search words to search across files AND folders(!) directly from the CMD-F search function
With this simple system it is so easy to have the 4 million samples completely under control and to work really emotionally in the flow.
Right in this moment I would like a "Reggae Snare", for example. CMD+F and "reggae snare" and Live could find a file right here:
Samples/Niche Audio/Dub & Reggae/Single Hits/Drums/Snares/77892snare.wav
The file would be found because the name Reggae and Snare are in the path, although you didn't even have to tag anything here! Add only one hashtag to the parent folder if the name itself is not clear enough.
With Cubase 9.5 this works incredibly well - but Cubase can't handle the 4 TB - the search goes on forever. Reaper does this fine, but searches every time (no indexing) and Bitwig makes it felt almost in real time including my whole 4 TB of samples.
PS: Why the hell do you have or need 4 million samples? If you've been making music for 20 years and are a collector, hunter and field recorder, then you accumulate a lot. It's enough to own the legendary samples.kb6.de donation ware sample library, that's a library with over 32,000 samples. Then you buy Drums Overkill from Best Service and you have another 27,000 drum samples on the record. And these are only two libraries with more than 50,000 files. I mean, the Ableton Live Suite content alone is over 70GB in size. Whether this is healthy or not is another question. But with this simple system, that the main folder of the sample pack has a revealing name - you can find almost anything.
Sorry for the long post. Here's a synthesizer cat: