Polish layout for physical USB keyboard in Oreo 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.

EDIT: This question is about Motorola Moto Z2 Play, which has an unmodified, stock version of Android 8.0 Oreo and such version doesn't have "Polish" physical keyboard layout. This question does not deal with devices provided by any other manufacturer, with modified Android, where "Polish" physical keyboard layout can be available.
edit i am using a nokia 6.1 runing a version of stock android 9 pie

i set my English UK keyboard to polish and Ukrainian layouts i was able to get Ukrainian input working by following this 
cannot change languange on external keyboard

but i could only get a few polish letters to work 
can you type in your native language with the on screen keyboard?

try going to settings and search for languages press languages and input press add language and your language should be there
then try the keyboard again