When i open kate from terminal, i get multiple messages so How do i get rid of those messages?

$ kate
Icon theme "gnome" not found.
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Icon theme "gnome" not found.
Icon theme "gnome" not found.
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Icon theme "gnome" not found.
Hspell: can't open /usr/share/hspell/hebrew.wgz.sizes.
kf.sonnet.clients.hspell: HSpellDict::HSpellDict: Init failed
Hspell: can't open /usr/share/hspell/hebrew.wgz.sizes.
kf.sonnet.clients.hspell: HSpellDict::HSpellDict: Init failed
inotify_add_watch(/var/lib/samba/usershares) failed: (Permission denied)
Qt: Session management error: networkIdsList argument is NULL
Icon theme "gnome" not found.
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Icon theme "gnome" not found.
Icon theme "gnome" not found.
Icon theme "ubuntu-mono-dark" not found.
Icon theme "Mint-X" not found.
Icon theme "elementary" not found.
Icon theme "gnome" not found.

These error messages indicate that one or more icon theme packages are not found.

I saw a very similar error to yours on my copy of Lubuntu 20.04 when starting nvim-qt and I fixed the issue by installing the missing package.

user@host:~$ nvim-qt
user@host:~$ Icon theme "elementary" not found.

user@host:~$ sudo su -
root@host:~# apt search elementary-icon-theme
Sorting... Done
Full Text Search... Done
elementary-icon-theme/focal,focal 2.7.1-0ubuntu7 all
  simple and appealing Tango-styled icon theme

root@host:~# apt install elementary-icon-theme
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following NEW packages will be installed:
  elementary-icon-theme
0 upgraded, 1 newly installed, 0 to remove and 0 not upgraded.
Need to get 1,984 kB of archives.
After this operation, 32.5 MB of additional disk space will be used.
Get:1 http://archive.ubuntu.com/ubuntu focal/universe amd64 elementary-icon-theme all 2.7.1-0ubuntu7 [1,984 kB]
Fetched 1,984 kB in 2s (1,134 kB/s)              
Selecting previously unselected package elementary-icon-theme.
(Reading database ... 278482 files and directories currently installed.)
Preparing to unpack .../elementary-icon-theme_2.7.1-0ubuntu7_all.deb ...
Unpacking elementary-icon-theme (2.7.1-0ubuntu7) ...
Setting up elementary-icon-theme (2.7.1-0ubuntu7) ...
gtk-update-icon-cache: The generated cache was invalid.
WARNING: icon cache generation failed for /usr/share/icons/elementary
root@host:~# exit
logout
user@host:~$ ls -al /usr/share/icons/elementary
total 276
drwxr-xr-x 16 root root   4096 Jan 23 21:41 .
drwxr-xr-x 22 root root   4096 Jan 23 21:41 ..
drwxr-xr-x  9 root root   4096 Jan 23 21:41 actions
drwxr-xr-x  9 root root   4096 Jan 23 21:41 animations
drwxr-xr-x  9 root root   4096 Jan 23 21:41 apps
-rw-r--r--  1 root root    878 Dec  5  2010 AUTHORS
drwxr-xr-x  9 root root   4096 Jan 23 21:41 categories
-rw-r--r--  1 root root    142 Feb 21  2011 CONTRIBUTORS
drwxr-xr-x  9 root root   4096 Jan 23 21:41 devices
drwxr-xr-x  9 root root   4096 Jan 23 21:41 emblems
-rw-r--r--  1 root root 197800 Jan 23 21:41 .icon-theme.cache
-rw-r--r--  1 root root   4932 Mar 24  2011 index.theme
drwxr-xr-x  9 root root   4096 Jan 23 21:41 mimes
drwxr-xr-x  6 root root   4096 Jan 23 21:41 notifications
drwxr-xr-x  6 root root   4096 Jan 23 21:41 panel
drwxr-xr-x  9 root root   4096 Jan 23 21:41 places
drwxr-xr-x  4 root root   4096 Jan 23 21:41 social
drwxr-xr-x 10 root root   4096 Jan 23 21:41 status
drwxr-xr-x  7 root root   4096 Jan 23 21:41 stock
drwxr-xr-x  3 root root   4096 Jan 23 21:41 tools
user@host:~$ nvim-qt
user@host:~$ 

I am not sure why installation threw this WARNING: icon cache generation failed for /usr/share/icons/elementary but when I ran nvim-qt subsequent times, that initial error no longer showed up.

Are these messages in the terminal window when you start it by typing kate? If so, if the editor works correctly, you can ignore those. Practically every program started from the terminal has some sort of harmless messages it spits out.

Ignore the messages if there is no problem. If the program works, they're harmless. They only matter if you're having some problem. Try starting some other programs from the terminal.

There will always be some sort of messages: such and such is missing, can't be found, no entry in some file, or other more cryptic messages. Trying to make them go away is like trying to make yourself stop dreaming!