It works in QGIS 3.10. It will most likely also work in 3.4.6 since it says
"SLYR also functions as a QGIS plugin (for QGIS >= 3.2)"
on the SLYR homepage on github.
After downloading slyr-master.zip from https://github.com/nyalldawson/slyr, unzip it and open the slyr-master folder. Here you'll find another slyr-folder. Copy and paste only this folder into C:\Users...\AppData\Roaming\QGIS\QGIS3\profiles\default\python\plugins.
In QGIS, go to Plugins–Manage and Install Plugins, In the Installed tab SLYR will be listed. Turn it on (checked).
Download the mdbtools (mdbtools-win-master.zip) mentioned in https://github.com/nyalldawson/slyr
"All tools require the command line mdbtools for handling the .style
database files. Binaries of these can be downloaded from
https://github.com/lsgunth/mdbtools-win, and they should be extracted
and available in the Windows path."
Unzip mdbtools-win-master.zip and copy the filepath to the unzipped folder mdbtools-win-master.
In QGIS, open Settings–Options–Processing. Click on Providers and SLYR and paste in the mdbtools-filepath in the Location-field. Click OK.
Now, you're ready to use SLYR.
Open the ToolBox (Processing–Toolbox or just press Ctrl-Alt-T). At the bottom you'll find SLYR, open SLYR–Style databases and choose the preferred tool, e.g. "Convert ESRI style to QGIS XML".
Choose the ArcGIS style-file to be converted. Click Run.
Then go to Settings–Style manager and import the XML-file just created. Click Import/Export and navigate to the XML-file. You may add additional tags. Click Select all (or just select the symbols you want) followed by Import.
In the Tags-list, choose one of the tags given previously (e.g. arcgis or forestry). The forestry styles appears.
Now I have access to all the styles from Layer styling-panel. The symbols available will change according to the geometry of the layer. E.g. choose the arcgis style from the list in the Style manager-list for a point file: