Could not see NAT entry in Cisco Router

Beside typo in regex part:
- some other device is performing NAT

Yes, actually that network (let's say 192.168.77.0/24) was NAT over a pool of IP public (overload) and we configure static NAT a host (192.168.77.19) to use another public IP address.

When I issued command "show ip nat translations | inc 192.168.77.21", I could see the NAT translations via that IP public but could not find it in "show run" command. So is that Okay? or is that a bug? Can we fix it?

NAT configuration should be present in running configuration (even if it part of some VRF, and not part of global configuration), otherwise it should not NAT traffic. Maybe IOS do not accept space in REGEX (maybe should be written as sh run | i ip_nat

Check running configuration without REGEX, or try to issue just
sh run | i nat

If there is no NAT statements in running configuration, please, check if your traffic is tunneled. That would be the case if your traffic is sent to some other location and then sent to ISP from that location (being natted there).

Not sure how entry that was not there can be deleted.
;)
You're welcome.

Generally, there is no possibility to delete statement that is not present in configuration and re-add it.
Either, statement was present in configuration or not.