Hi @drhemantkumar
If you can't hear in either the earpiece receiver or the loudspeaker when also using the phone in safe mode, the next thing to try would be to ''factory data reset'' the phone and then test if it works OK to determine whether it is a software problem or a hardware problem. (See ''Resetting the Device'' ''on p.193 of the'' [https://downloadcenter.samsung.com/content/UM/202311/20231128160732855/SM-F936B_F926B_UM_EU_UU_Eng_Rev.1.0_231026.pdf|user manual])
''Be aware that a ***factory data reset will erase all your data and downloaded apps***. It will reset the phone to its default factory condition. It will be like when you first bought it. If you decide to do this then ***backup the phone to the cloud or a computer*** using the phone's backup feature ***before you perform the factory data reset.*** (See p.156 of the user manual)''
''Also if the phone has a Google or Samsung account associated with it, then ***you will need to remember the account user name and password*** as it has to be entered after the reset so that you can access and set up the phone again. This is due to the FRP lock (factory reset protection) that has been enabled by the reset. This is a security feature in Android phones in the event that the phone is lost or stolen''
It it works OK after a factory reset then you can restore the phone to what is was before the reset using the backup you made earlier. ''(See Restoring your device on p.157 of the user manual)''
If it still doesn't work after a factory data reset then it's a hardware problem and the [https://www.repairlap.com/threads/samsung-galaxy-z-fold-3-sm-f926u-service-manual.20951/|service manual] would need to be purchased to help find out what was wrong. Alternatively contact a reputable, professional mobile phone repair service (Samsung?) and ask for a quote to repair the phone.