Translation:I did not understand what my boss wanted from me.
It should not. Czech and English have different approach to tense sequencing. https://www.helpforenglish.cz/article/2011021902-casova-souslednost-tabulka
I understand this sentence to mean 'I did not understand what my boss wants from me'. That is a continuing state of affars rather than 'what my boss wanted from me'. A completed state now finished. I am not interested in the English technacalities only how to express myself in Czech. As you may be aware I am a 78 year old native UK english speaker. Good luck in the new year and I do really appreciate your help.
Because in Czech in complex sentences you can use Past + Present if dependent clause says about the same time as main clause. But in English you must use Past + Past. You can see the table in kacenka9 post upper - it shows how dependend clause in Present transforms to the Past.
I don't quite agree about the English... If the subject of the dependent clause is different from the main, then it depends on what is being emphasized. If the dependent clause refers to an unchanging condition, then past--present is fine: "when I moved here I didn't realize that it always rains"... Though rained would be ok too. If the subject of both clauses is the same, I agree that you need tense agreement.