You can check this thread out → Tutorial: 2020 North America 2.20 Map Installation (Stand-Alone without Reformat) with Updated NAV_Voice 06/21/2021
It’s for NA, but will give you information about what needs to be done.
Since your unit is EU (64GB), I would think the space limitation described in the NA thread might not apply, but not 100% sure.
If you do not want to proceed manually, you can set Syn3updater to create the USB in a single stage.
Otherwise, you need to follow the tutorial to install the 3 files in multiple steps.
You could use Syn3updater to do so by creating multiple UBS for the multiple files.
If you check the file selection list in Syn3updater, you will find VOICE_NAV files…
And those should be autoinstalled.