1. Introduction

2. COSMOS as a basis to simulate Euclid galaxies  
2.2. Galaxy physical parameters obtained with SED fitting

3. Simulation of Euclid, Rubin-LSST, H20 survey, and Spitzer photometry of \( z=1–8 \) galaxies

4. Results  
4.2. Identification of \( z>6 \) contaminants  
4.3. Separation of contaminants from true \( z>6 \) galaxies  
4.4. The nature of the \( z>6 \) contaminants

5. Complementary tests based on a faint mock galaxy sample

6. Discussion  
6.1. Validity of the simulated high-z solutions  
6.2. Independent check of contamination fraction with COSMOS2020  
6.3. Identification of \( z>6 \) galaxies from colour-colour diagrams alone  
6.4. Possible caveats in this work

7. Summary and conclusions