Hi @marianochaves
Does the spot also appear on pictures taken by the camera and then downloaded and viewed on a PC or monitor?
If not, then there may be a problem with the LCD screen or the motherboard.
Only way to isolate where it is, i.e. LCD screen or motherboard, may be to temporarily replace the LCD screen and check if it is still there or not.
Here's a [https://www.youtube.com/watch?v=meheyvR4LpI|video] that ''may'' help with accessing the camera's LCD screen.
Search online for [https://www.google.com/search?client=firefox-b-d&q=lfuji+x-a3+lcd+screen|Fujifilm X-A3 LCD screen] (supplier examples only) to find suppliers that suit you best.