I was birding in the mountains of Romania last week (700 - 1000 m, coniferous forest) and saw a lot of these juvenile birds. my best guess is European Robin, but I think Red-breasted Flycatcher and Dunnock juveniles are also likely. what do you think?
checklist 1: https://ebird.org/view/checklist/S59419908
checklist 2: https://ebird.org/view/checklist/S59392296
a few photos: