Sharepoint document library over 100k files

We have faced issues with large libraries especially if you employ a complex folder structure, I would suggest creating a library template that you can re-use to breakdown the files, you could then create a custom solution (classic search page, Power app, etc.) To search all your documents and configure in a way that works for your organisation although with some tweaks the built in search can be very robust. If using on prem, you may want to consider provisioning a separate content database aswell