Hi just configurated my 760gis 5ethernet port POE for unifi AP-LR - connet directlly and this is working with basic powerr suppy 12V 1,2A (box supply).
The router became really hot and I wonder is this normal? I got POE injector for unifi, but if that solution working...
When i swith powerr supply for 54v the effect is the same - router is hot,
Witout POE is almost cold - whot do you thing? In that way(POE)I can damage my device(router)?

First of all, your MikroTik device is code [RB760iGS] and Ubiquiti is code [UAP-LR].

The RB760iGS PoE can supply 500 mA between 18-57 V.
The UAP-LR requires 6 W of power.
This is 333 mA in the worst case.
So you're not destroying the device.

Since there is no information on PoE capabilities below 18 V (???), and the UAP-LR load can be as high as 500 mA at 12 V, so using a 12 V adapter is not recommended!

My unifi is Ubiquiti Networks UAP-AC-LR and it is powered 24v,
Router power supply is 24v 1,2A
Why the router is so hot?