For a long time I've been wondering, can WiFi and mobile Internet on my phone be turned on at the same time? I noticed that in this case the Internet works worse, is there an explanation or is it a coincidence?
I apologize if I am asking a question in the wrong section.
It depends on a few factors but I have noticed this can happen if you use 3g cell with this mix, 4g cell and wifi did not show this 'issue'. It may also be an ipv6 thing of your cellphone, mixing ipv6 cell with ipv4 wifi could be a problem.
I haven't seen a mainstream phone that *COULDN'T* connect to WiFi *and* cellular data at the same time in over 10 years. Are you saying you manually shut one service off and the other on all the time?
I have even seen (or looked for) the option the specify "prefer WiFi over Data" in a decade, or if it exists anymore.
Typically, at least in my experience, you setup both. If WiFi is available (you have network credentials), it will be used. If there is an issue, then the automatic fallback is to use your carriers data services. This is to save you on data charges. Some apps or functions can be restricted so they are locked in one mode or the other (Google play for example) so that updates won't eat into you paid data limits.