iPhone Xs Max turned off. It doesn't turn ON anymore after trying force restart or charging it for 12+ hours

Me & my spouse both own iPhone Xs Max (64 GB) versions purchased in 2019. Her phone died after using for just over an year (doesn't turn ON anymore after trying force restart or charging it for 12+ hours). Had taken it to an authorized iPhone service center in India, I was told that its motherboard needs to be replaced which would almost cost me a new phone.

Now my iPhone died a similar death last week. Both phones have been carefully used & I don't understand how could this happen.