It may be simplest to move it to a hosted server. Depending on the length of outages, your comfort with electrical things, and your budget, you could get a bigger battery and use the inverter in the UPS (there are caveats-the inverter in the UPS is not rated for higher end of its load past the battery capacity it’s got and may burn itself out, and the charger may not work properly with the larger battery or with different chemistry), or get a battery/inverter box like a Ecoflow or that sort of thing. Solar may be a good bet too.

I don’t know about matrix but failing over between public IPs probably requires a HA sync of some type and also DNS failover.