Upgrading visual svn server from 3.7.0 using svn 1.9.7 - how?

We are using this setup:
- Main server is running on Windows Server 16 Standard using VisualSVN
version 3.7.0, which apparently uses svn 1.9.7

- The server is using svnsync nightly to synchronize over the Internet
to a mirror SVN server version 1.9.7 running on Ubuntu 18.04 Server on
a different location entirely.
No user operations are allowed on the mirror, it is just a backup.

My problem is this:
The VisualSVN server is seriously out of date and needs to be
upgraded. In its own management console it suggests upgrading to 4.2.2
but does not say which version of svn will then be running.
In fact it seems like they are intentionally hiding the svn version in
their web pages.. :(

And I suspect that there might be problems concerning the svnsync
commands if the backup mirror server is not upgraded to the same svn
version, right?
But how do I do that on Ubuntu when I cannot find out which svn
version they use?

Or does it not matter, i.e. can the main and mirror servers be using
different svn versions?

-- 
Bo Berglund
Developer in Sweden