First FreeTube is a known OpenSource desktop client for YouTube, there isn't a security risk (false positive from your AV). Maybe this and also cloudtube and other like yewtube are also OpenSource and forks from Invidious give alerts from certain companies, because permits to download YT vids.
In Piped there isn't such option, it use it's own engine to stream YT vids, without using the googlevideoAPI, like the others, this permits it to control better the content and block ads and trackers from Google, also jump the invideo sponsor blocks and intros. It has a very impresive settings page in this sense. You can create an account (nick, mail) which permits to subscribe your prefered channels and shows new videos of these (Feed).
Well, certainly there are a lot of more search engines as only Google, Bing, and Yahoo out there. The AI search engine you mencioned is Andi, privacy oriented and don't show a lot of results, it is different, Andi is an AI who understand the concept of your search and shows the most relevant results respect of your search, you can really chat with it. Something like Alexa, but without trackers, loggings and ads, 100% private.
I use Andi for my first searches, before I use the others I use. To add Andi to your search engines in your browser to permit to search with your search or adress bar, use this code to put it as search engine in the list of your browser
https://andisearch.com/?query=%s
You'll find a very complete list of search engines in a post from oen of the user in the Vivaldi Forum, including the codes to use them in the browser from the adress or search bar
https://forum.vivaldi.net/topic/46609/guide-vivaldi-search-engines-collection