President Zelenskyy does not have the authority to cede any Ukrainian land under their constitution. Any land concessions require a public vote.
President Putin has also made claims the Zelenskyy cannot sign any agreements because his term has ended. This is not true; Ukraine’s parliament (the Verkhovna Rada) has formally and legally extended President Volodymyr Zelenskyy’s mandate until martial law is lifted. This means his presidency continues beyond the normal five‑year term because elections cannot be held during wartime.
The question then begs of itself, if elections cannot be held during wartime – by what method would the public approve the land concession? I smell the makings of a constitutional exception.
FYI.