Cannot add .onion search engine when equivalent clearnet is present
Adding e.g. https://search.snopyta.org/ as a search engine prevents its .onion equivalent from being added, http://yra4tke2pwcnatxjkufpw6kvebu3h3ti2jca2lcdpgx3mpwol326lzid.onion/, and there is no notification to the user for the cause of this issue; the 'Add Search Engine' option is completely absent and there is no practical way of knowing that this is the cause for the issue from the user's perspective.
The workaround is to remove the clearnet search engine manually and then add the .onion version.
This is important not only because adding the .onion version avoids clearnet connections but also because when enabling redirects from clearnet to .onion POST requests are lost, so searx is not only less private but practically useless as it redirects to the .onion with the search parameters lost.