This will probably not be enough. Because if your PC is running at full load, it will "say" more than 540W. It would be helpful to know which power supply you have, the UPS should have the same maximum output as your power supply (otherwise the power supply can only draw as much power as the UPS delivers). The graphics card and CPU alone draw more than 540W under full load (according to digitec, up to approx. 700W and this does not include fans and other components). It also plays a role what your goal of the UPS is, should the operation be ensured in the event of a short power failure, or should the UPS also last longer? Then it is no longer the maximum output power but the capacity of the battery that is decisive.

Probably not, the graphics card alone can achieve the 540W on its own.