Who said it's illegal?
How about R’ Chaim Kanievsky? Is he holy enough for you?
No? How about R’ Gershon Edelstein, who specifically had a picture publicized of him davening b’yechidus “so that others should see, and understand that if I can daven without a minyan, then so should they”?!
Wake up, people. It’s not about the black-and-white of a government decree. The government is not your freaking babysitter. Just because you found a loophole in something they said, that doesn’t necessarily make it suddenly healthy and wise to do so!!!! Just because you’re allowed to buy cigarettes when you’re older than 18, for example, that doesn’t mean that smoking is healthy for you... it simply means that there’s a limit to how much the government can be your babysitter, and after which point you have to GROW THE $&@% UP and take responsibility for your own actions.
If this is something that EVERY MEDICAL PROFESSIONAL HAS SAID SHOULD NOT BE DONE, and ALMOST EVERY RABBINICAL AUTHORITY OF NOTE HAS AGREED WITH, to the point that RAV CHAIM KANIEVSKY EXPLICITLY SAID THAT YOU CAN REPORT PEOPLE WHO MAKE ILLEGAL MINYANIM TO THE AUTHORITIES, then why do you have to think you’re smarter?! Why?! Why?! WHY?!?!
WHY?!?!?! Did not enough Jews die yet to convince you?!?!
If you contract COVID-19 while attending a minyan these days (even if you found a “loophole” in the secular law for that) and die from it, do you really think you’ll be welcomed into Shamayim with open arms as someone who died “al kiddush Hashem”?! Or do you think you’ll be getting the express elevator to the basement, for violating divrei chachamim and explicitly going against the words of virtually every gadol of note b’zman hazeh?!
In summary... my main point is: it’s not just government laws that can make something illegal. Commands from our gedolim can make something “illegal” for a G-d fearing Jew, too. And even if you find a valid “loophole”, you’re still an idiot, and your blood - and the blood of others - is on your hands.