  Large format arrays of transition edge sensor (TES) are crucial for the next
generation of X-ray space observatories. Such arrays are required to achieve an
energy resolution of $\mathrm{\Delta}E<$3 eV full-width-half-maximum (FWHM) in
the soft X-ray energy range. We are currently developing X-ray microcalorimeter
arrays as a backup option for the X-IFU instrument on board of ATHENA space
telescope, led by ESA and foreseen to be launched in 2031. In this
contribution, we report on the development and the characterization of a
uniform 32$\times$32 pixel array with (length$\times $width) 140$\times$30
$\mu$m$^2$ TiAu TESs, which have \textcolor{black}{a 2.3 $\mu$m} thick Au
absorber for X-ray photons. The pixels have a typical normal resistance
$R_\mathrm{n}$ = 121 m$\Omega$ and a critical temperature $T_\mathrm{c}\sim$ 90
mK. We performed extensive measurements on 60 pixels out of the array in order
to show the uniformity of the array. We obtained an energy resolutions between
2.4 and 2.6 eV (FWHM) at 5.9 keV, measured in a single-pixel mode at AC bias
frequencies ranging from 1 to 5 MHz, with a frequency domain multiplexing (FDM)
readout system, which is developed at SRON/VTT. We also present the detector
energy resolution at X-ray with different photon energies generated by a
modulated external X-ray source from 1.45 keV up to 8.9 keV. Multiplexing
readout across several pixels has also been performed to evaluate the impact of
the thermal crosstalk to the instrument's energy resolution budget requirement.
This value results in a derived requirement, for the first neighbour, that is
less than 1$\times$10$^{-3}$ when considering the ratio between the amplitude
of the crosstalk signal to an X-ray pulse (for example at 5.9 keV)
