Missing component identification
Can anyone help me to understand what component could be the missing
one?

I think there's a good basis for believing the capacitor was deliberately de-soldered in order to improve the tuning of the antenna or oscillator that it uses. Many designs leave space to add components through a &quot;select-on-test&quot; process and, quite often some components are fitted and then removed in the same process.

I thought a capacitor similar to others close but I'm not sure.

Given the type of circuit, more than likely it is a capacitor but there's no-way that it might be similar to others that surround it.