Custom search engines without relying on automated system to pick them up

I am hosting my private SearXNG instance in my homelab, but no matter what i do i can’t get it to show up on mobile. On the other hand on desktop i can simply add a custom one by inputting the query URL.

I would love to see the same (or comparable) level of customization of the search engine to mobile: a simple ‘+’ icon and a query URL string to input, simple and clean without convoluted and often unreliable automated mechanisms.