Your old Gimp scripts and plugins will not work with Gimp 3.0 - that includes PSPI which goes back to Gimp 2.8 days.
Those .8bf filters are a particular sub-set. Best bet if you want to use them is try IrfanView and export the result for use in Gimp 3.0
Using Widows 11. AFAIK you can have both Gimp 2.10 and Gimp 3.0 installed. Use Gimp 2.10
Edit: Consider alternatives. The gmic_gimp_qt plugin is available for Windows Gimp 3.0 http://www.gmic.eu That has 600+ filters Probably has an equivalent for your requirements
Those .8bf filters are a particular sub-set. Best bet if you want to use them is try IrfanView and export the result for use in Gimp 3.0
Using Widows 11. AFAIK you can have both Gimp 2.10 and Gimp 3.0 installed. Use Gimp 2.10
Edit: Consider alternatives. The gmic_gimp_qt plugin is available for Windows Gimp 3.0 http://www.gmic.eu That has 600+ filters Probably has an equivalent for your requirements