Not trying to be rude but just because search engines added random things to their service doesnt mean it is a good idea to do it. I'd suggest you just get used to using literally any calculator of the likely 5-10 devices in your house that have them. Every laptop, pc, phone has a calculator and some people who regularly need them (like myself) even have standalone ones.
For the stock prices you can use a stock app on most phones or a website bookmark in any browser.
The comfort of big tech is one major reason they have a death grip on our society. We have to work and think like hell every day. Of course it is easiest to streamline such basic things. But it also locks you in.
It is sinister because instead we could just work less and still have more than any of our ancestors ever dreamt of but instead the surplus value gets siphoned off.
In linux, open a terminal, and type "python". There you have a great calculator. You can create a shortcut to speed it up. Pretty sure there is a module for stock stalking too.
DDG can do lots of conversions and translations. But if you use linux and KDE, the start menu's search bar does that too, and it is extensible with plugins
DDG should do the currency conversions. But, you know your phone has a calculator that doesn't send data anywhere, right? Why wait for the server to do math when you can do it all in your hand?