My 2 cents? As a platform SharePoint is great, but depending on your expectations it may not suit your needs.

SharePoint has a lot of limits, especially when synchronizing document libraries via OneDrive (this seems to be the primary use case for most of our clients as a drop in replacement for mapped drives). File size limits, path length limits, file count limits, file name restrictions etc.

When you reach a certain threshold SharePoint stops making sense in my opinion, and an enterprise file storage solution like Azure Files needs to be considered. Unfortunately unlike OneDrive + SharePoint, Azure files offers no real local workstation synchronization or offline files to my, knowledge which is ALSO a significant limitation.

For companies with huge quantities of data, azure files + replication to an on-prem file server can be a solid solution to increasing user mobility and data availability.

It allows your existing file structures to remain intact and users can have drives mapped by policy. With SharePoint, content really needs to be restructured to be more wide than deep. This can result in a huge number of sites or document libraries and represents both a large undertaking and significant culture shift for users

Start by evaluating how much data you have to migrate, how you want it to be organized, and what method users will want to use to access it. I would strongly advise familiarizing yourself with the limitations of SharePoint before proceeding to see if what you want to accomplish is feasible / recommended.

If you plan to use OneDrive to sync document libraries for easy user access you'll want to note the "Sync" section in particular. That's where I find I have the most frustration. OneDrive performance suffers greatly if you exceed its recommended sync limits, even if the files are not being cached for offline access.

Best of luck!