Download "Homepage for Safari" by Ahnaf Mahmud on the App Store

Open the app and paste this link:

https://sites.google.com/view/skildalindustriessearchengine/skildal-industries-search-engine

And click "Save"

Open settings and search for "Safari Extentions"

You should see "Homepage" on the list. Click on the app

Make sure that "allow extention" is on. Optional turn on "allow in incognito window" and make sure that "open new tabs" is set to "with "homepage""

Open Safari and open a new tab, and then the search engine should work