FYI, Kagi has an app that provides an extension that takes over the DDG domain (and maybe other default search engine domains) to redirect searches to Kagi. This still leaks the query to the original search engine, but it's better than nothing.
Yeah, I use these bangs too, but it also means that every query is sent to 2x search engines - DDG and the destination search.
There is a Safari extension called xSearch [0] which implements bangs client side, but I uninstalled it because I noticed weird TLS errors on a few sites while it was running, and I'm generally uncomfortable with the level of access required for it to function.
Still haven’t heard from them but it’s worth a try.
https://duckduckgo.com/newbang
Adding other browsers to DDG bangs would somewhat solve the problem, at least for me with Kagi.