It's all your fault as you put me on to Lua smile

It's just using the Lua os.execute function, then inserts the media

Code:
os.execute([[cmd.exe /C " C:\ProgramData\Anaconda3\Scripts\activate.bat & echo processing please wait... & cd ]] .. script_path2 ..[[ & spleeter separate -i "]] .. filename .. [[" -p spleeter:5stems -o "]] .. filepath .. [[spleeter_output"]]) 

reaper.InsertMedia( filepath .. "spleeter_output//" .. folder_name .. "//bass.wav", 1 )
reaper.InsertMedia( filepath .. "spleeter_output//" .. folder_name .. "//drums.wav", 1 )
reaper.InsertMedia( filepath .. "spleeter_output//" .. folder_name .. "//other.wav", 1 )
reaper.InsertMedia( filepath .. "spleeter_output//" .. folder_name .. "//piano.wav", 1 )
reaper.InsertMedia( filepath .. "spleeter_output//" .. folder_name .. "//vocals.wav", 1 )