Why are Ukrainian and European leaders concerned about the US-Russia talks in Riyadh?

Ukrainian and European leaders are expressing significant concern about the US-Russia talks in Riyadh because they fear that Trump could negotiate a hasty deal with Russia that overlooks their security interests. They worry such an agreement might reward Russia while allowing Putin to continue posing threats to Ukraine and potentially other countries in the future. Despite Russia having managed to endure sanctions, the way these talks have proceeded without Ukrainian or European participation has raised apprehension. Both Ukraine and European officials are particularly troubled by their exclusion from negotiations that directly impact their security, suggesting a potential sidelining of their perspectives in favor of bilateral US-Russia arrangements.