Up until Android 8.0 / Oreo (haven't got chance to test this issue under 9.0 / Pie) there is no Polish layout for physical USB keyboard and writing Polish national letter (i.e. using Right Alt key) is not possible in Android with physical keyboard connected through USB and micro USB OTG cable.
Is there anything I can do to resolve this problem? Some option for installing missing layouts?
Supporting, OT and philosophic question: Is this some kind of political isolation of my country by Google / Android developers or an ostracism? I have carefully checked that there are keyboard layouts for each and every neighboring country that surrounds Poland -- i.e. German, Czech, Slovak, Ukrainian, Latvian, Lithuanian and Russian. But there is no for Poland.