Install the (monster) nik executable to the default location C:\Program Files\Google\Nik Collection.
Gimp does not use the .8bf PS plugins, make sure you have the 64 bit executable in the Nik folders installed.
Not worth modifying the shellout plugin - all the work has already been done.
Use the python plugins that Partha Bagchi has in his version of Gimp - zip attached.
Unzip, put the six python plugins in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\plug-ins.
Find the plugins in the Gimp filters menu.
A 2 minute demo of the above
https://youtu.be/u309pfmGaKwJust my opinion

These effects are largely achievable with the gmic_gimp_qt plugin.