Long-term X-ray and UV light curves for J0456−20. The coloured regions represent the four phases defined in Sect. 3.1 based on the X-ray light curve: the plateau phase (P_X, plat, light cyan), the rapid drop phase (P_X, drop, light blue), the faint phase (P_X, faint, light yellow), and the rising phase (P_X, rise, light green). Upper panel: Red points are the unabsorbed intrinsic 0.2 − 2.0 keV X-ray light curve from eROSITA (hexagons), Swift/XRT (squares), NICER (circles), and XMM-Newton (stars). The error bars indicate 90% uncertainties. The 3σ flux and luminosity upper limits are shown with downward arrows. The dashed black line shows the best-fitting power-law model, f_rs(t) ∝ (t − t₀)^β, where t₀ = 59377 ± 9 and β = 2.3 ± 0.7 (quoted uncertainties are at 1σ confidence level), during the rise phase. The dashed grey line shows the same model, but shifted by 223 days. Bottom panel: Long-term UV light curves from Swift/UVOT UVM2 (red squares) and XMM-Newton/OM UVM2 (red stars). The error bars mark the 1σ uncertainties. Empty squares with downward arrows indicate 3σ upper limits. The vertical dashed-dotted lines mark the dates of the five ATCA radio observations (black: non-detections; blue: detections), and the upward arrows marked with an S indicate the dates when optical spectra were obtained.