Batch - findstr special characters

I try to find and move all files with the character "{" (without the quotes) for example filename{{xyz}}.txt

My Code:

@echo OFF
setlocal enableextensions disabledelayedexpansion

set "source=C:UsersOLD*.txt"
set "target=C:UsersNEW"
set "searchString=}"

set "found="
for /f "delims=" %%a in ('
    findstr /m /i /l /c:"%searchString%" "%source%" 2^>nul 
') do (
    if not defined found set "found=1"
    move "%%a" "%target%"
)

if not defined found (
    echo not found
)

This script found all characters, unfortunately not that one what I need {. So now I will ask here for help.

Best regs