Can you please check the phone's settings that fast charging is still activated.
Also are you able to try another Samsung charger cord and charging plug as a process of elimination.
Look inside the charging port with a torch to check there isn't a built up of debris.
To add a Samsung Experience Store or Samsung Service Centre can take a look too @gemini30
I wish you all the best with this situation.
Current Phone ~Samsung Note 20 Ultra 5G SM-N9860_256Gb SnapDragon 865+ Samsung One Ui 3.0/ Android 11.