I come from Manjaro. My first time on real Arch.
When I start Welcome menu. No update button works.
:: Sincronizando las bases de datos de los paquetes…
error: no se han podido sincronizar todas las bases de datos (no hay servidores configurados para el repositorio)
→ error refrescando las bases de datos - exit status 1
DE: Plasma 5.27.4
WM: KWin
Terminal: konsole
CPU: Intel i3 M 370 (4) @ 2.399GHz
GPU: Intel Core Processor
What is the content of your /etc/pacman.conf ?
Run the following command, copy the terminal output, paste it into your replay and press Ctrl-E to format:
cat /etc/pacman.conf
Do you have the package reflector-simple installed?
Error: all databases have not been synchronized (there are no configured servers for the repository)
could be mirrorlist update fails and its empty… ?
cat /etc/pacman.d/mirrorlist shows mirrors or garbage?
If you want the easy way to get a very good mirror list, automatically sorted by speed, just run in the terminal
rate-mirrors arch | sudo tee /etc/pacman.d/mirrorlist
But first, make sure that the package rate-mirrors is installed.
You only need to do this when you notice package download speed being low. I do it maybe twice a year, but depending on where you are, you might need to do it a bit more often.
It’s much better than reflector, and infinitely better than the supposedly “simple” reflector.
The popup message is from reflector-simple and says “country code not found” 
In posted image, the terminal looks like the archlinux mirrorlist and includes several servers. 
The Simple goes Complicated 
Or you can use safesync
Welcome to the forum! 
Like some here say, we need to see the contents of
/etc/pacman.d/mirrorlist
Please show the contents of
/etc/pacman.d/endeavouros-mirrorlist
as well.
If they are OK, then you can update with command
sudo pacman -Syu
Thanks, for the answers.
cat /etc/pacman.conf
#
# /etc/pacman.conf
#
# See the pacman.conf(5) manpage for option and repository directives
#
# GENERAL OPTIONS
#
[options]
# The following paths are commented out with their default values listed.
# If you wish to use different paths, uncomment and update the paths.
#RootDir = /
#DBPath = /var/lib/pacman/
#CacheDir = /var/cache/pacman/pkg/
#LogFile = /var/log/pacman.log
#GPGDir = /etc/pacman.d/gnupg/
#HookDir = /etc/pacman.d/hooks/
HoldPkg = pacman glibc
#XferCommand = /usr/bin/curl -L -C - -f -o %o %u
#XferCommand = /usr/bin/wget --passive-ftp -c -O %o %u
#CleanMethod = KeepInstalled
#UseDelta = 0.7
Architecture = auto
# Pacman won't upgrade packages listed in IgnorePkg and members of IgnoreGroup
#IgnorePkg =
#IgnoreGroup =
#NoUpgrade =
#NoExtract =
# Misc options
#UseSyslog
Color
ILoveCandy
#NoProgressBar
#CheckSpace
VerbosePkgLists
DisableDownloadTimeout
ParallelDownloads = 5
# By default, pacman accepts packages signed by keys that its local keyring
# trusts (see pacman-key and its man page), as well as unsigned packages.
SigLevel = Required DatabaseOptional
LocalFileSigLevel = Optional
#RemoteFileSigLevel = Required
# NOTE: You must run `pacman-key --init` before first using pacman; the local
# keyring can then be populated with the keys of all official Arch Linux
# packagers with `pacman-key --populate archlinux`.
#
# REPOSITORIES
# - can be defined here or included from another file
# - pacman will search repositories in the order defined here
# - local/custom mirrors can be added here or in separate files
# - repositories listed first will take precedence when packages
# have identical names, regardless of version number
# - URLs will have $repo replaced by the name of the current repo
# - URLs will have $arch replaced by the name of the architecture
#
# Repository entries are of the format:
# [repo-name]
# Server = ServerName
# Include = IncludePath
#
# The header [repo-name] is crucial - it must be present and
# uncommented to enable the repo.
#
# The testing repositories are disabled by default. To enable, uncomment the
# repo name header and Include lines. You can add preferred servers immediately
# after the header, and they will be used before the default mirrors.
[endeavouros]
SigLevel = PackageRequired
Include = /etc/pacman.d/endeavouros-mirrorlist
#[testing]
#Include = /etc/pacman.d/mirrorlist
[core]
Include = /etc/pacman.d/mirrorlist
[extra]
Include = /etc/pacman.d/mirrorlist
#[community-testing]
#Include = /etc/pacman.d/mirrorlist
[community]
Include = /etc/pacman.d/mirrorlist
# If you want to run 32 bit applications on your x86_64 system,
# enable the multilib repositories as required here.
#[multilib-testing]
#Include = /etc/pacman.d/mirrorlist
[multilib]
Include = /etc/pacman.d/mirrorlist
# An example of a custom package repository. See the pacman manpage for
# tips on creating your own repositories.
#[custom]
#SigLevel = Optional TrustAll
#Server = file:///home/custompkgs
You didn’t check whether rate-mirrors was installed, right? 
I told you to check before running that command…
Well, you didn’t have it installed, so you’ve deleted your mirrorlist. Not a big problem, but still, just causing yourself unnecessary work.
Try running this:
reflector -a 10 --sort score | sudo tee /etc/pacman.d/mirrorlist
After that (if it was successful):
sudo pacman -Syyu
Open the mirrorlist in kate:
kate /etc/pacman.d/mirrorlist
It’s probably going to be empty.
With your web browser, go to https://archlinux.org/mirrorlist/ select your country and click the button Generate List. Copy and paste all the text you get from that web page.
Save the file (you’ll be prompted for your password). Then run
sudo pacman -Syyu
After that you can install rate-mirrors and repeat the same procedure to get the optimum mirrorlist.
need geoip and whois installed…
sudo pacman -S geoip whois
yes indeed this is a list not any executable … you missed to cat the file …
cat /etc/pacman.d/mirrorlist
Thank you all. Kresimir frog’s advice has helped me to solve the problem. 
Welcome to the EndeavourOS forum. I hope you enjoy your time here,
Please go to @Kresimir 's post that most helped you solve the problem. Then click on the “Solution” icon. This triggers the forum software to mark this Topic as solved, amongst other things.
Pudge
This. This right here.
Although this solved the problem of rating the mirrors my question is why doesn’t it work from the Welcome app. Shouldn’t geoip and whois already be installed? 
it should be there indeed… but it can be uninstalled by different reasons…
it will warn but it is optional may we consider making it a hard dependency for reflector simple? as if it dies not work without them installed?
:: reflector-simple optionally requires whois: optional alternative for finding country code
:: reflector-simple optionally requires geoip: optional alternative for finding country code
No way!
Well if it is used by Welcome and needed then should be installed.