The whole point of using AVX is for better performance. Emulating it with older instructions is going to be very slow. I very much doubt a game like Star Citizen will actually be playable with the 1090T regardless.
Though this is a terrible time to buy PC hardware, you really do need to upgrade for modern game titles.
Fortunately, some of the lower end parts are not too hard to find. A Ryzen 1600AF will run you about $150. A budget B450 board is another $75 or so, and 16GB of RAM $75 more. So that's $300 for a CPU setup that will run any game out there, and be insanely faster than your 1090T.
The only downside to such an upgrade is that it might make your GPU the bottleneck. You didn't mention what that is, but if it's anywhere near as old as your CPU, you won't be able to play any modern games with it, either. Finding a suitable upgrade for that will be a lot more difficult right now, due to supply chain issues.