Now I flashed the SD Card with Arch Linux (following instructions from https://archlinuxarm.org/platforms/armv8/broadcom/raspberry-pi-4 ), repeated the same steps and it worked.
I prefer Manjaro, will continue trying to make it work until I find a way or someone with more knowledge find the solution. 
As @Darksky only get it to work until reboot, I powered off, turned it on and tested again. Still works.
-` alarm@rainbow
.o+` -------------
`ooo/ OS: Arch Linux ARM armv7l
`+oooo: Host: Raspberry Pi 4 Model B Rev 1.1
`+oooooo: Kernel: 5.4.50-1-ARCH
-+oooooo+: Uptime: 4 mins
`/:-:++oooo+: Packages: 237 (pacman)
`/++++/+++++++: Shell: bash 5.0.17
`/++++++++++++++: Terminal: /dev/pts/0
`/+++ooooooooooooo/` CPU: BCM2711 (4) @ 1.500GHz
./ooosssso++osssssso+` Memory: 71MiB / 3837MiB
.oossssso-````/ossssss+`
-osssssso. :ssssssso.
:osssssss/ osssso+++.
/ossssssss/ +ssssooo/-
`/ossssso+/:- -:/+osssso+-
`+sso+:-` `.-/+oso:
`++:. `-/+/
.` `/
$ pstree
systemd-+-NetworkManager---2*[{NetworkManager}]
|-agetty
|-dbus-daemon
|-f2b/server---4*[{f2b/server}]
|-haveged
|-nginx---nginx
|-sshd---sshd---sshd---bash---pstree
|-systemd---(sd-pam)
|-systemd-journal
|-systemd-logind
|-systemd-network
|-systemd-resolve
|-systemd-timesyn---{systemd-timesyn}
|-systemd-udevd
`-wpa_supplicant
$ pacman -Si rspamd
Repository : community
Name : rspamd
Version : 2.5-2
Description : Fast, free and open-source spam filtering system
Architecture : armv7h
URL : https://rspamd.com
Licenses : BSD
Groups : None
Provides : None
Depends On : file glib2 glibc icu jemalloc libevent libsodium luajit openblas openssl pcre sqlite zlib
Optional Deps : redis: Redis cache and data storage
Conflicts With : None
Replaces : None
Download Size : 2.42 MiB
Installed Size : 8.52 MiB
Packager : Arch Linux ARM Build System <builder+xu4@archlinuxarm.org>
Build Date : Fri May 1 13:13:39 2020
Validated By : MD5 Sum SHA-256 Sum Signature
$ sudo systemctl status rspamd
* rspamd.service - rapid spam filtering system
Loaded: loaded (/usr/lib/systemd/system/rspamd.service; disabled; vendor preset: disabled)
Active: inactive (dead)
Docs: https://rspamd.com/doc/
$ sudo systemctl start rspamd
Jul 08 20:41:57 rainbow sudo[451]: alarm : TTY=pts/0 ; PWD=/home/alarm ; USER=root ; COMMAND=/usr/bin/systemctl start rspamd
Jul 08 20:41:57 rainbow sudo[451]: pam_unix(sudo:session): session opened for user root by alarm(uid=0)
Jul 08 20:41:57 rainbow systemd[1]: Started rapid spam filtering system.
$ sudo systemctl status rspamd
* rspamd.service - rapid spam filtering system
Loaded: loaded (/usr/lib/systemd/system/rspamd.service; disabled; vendor preset: disabled)
Active: active (running) since Wed 2020-07-08 20:41:57 -03; 1min 43s ago
Docs: https://rspamd.com/doc/
Main PID: 454 (rspamd)
Tasks: 5 (limit: 4915)
CGroup: /system.slice/rspamd.service
|-454 rspamd: main process
|-456 rspamd: rspamd_proxy process (localhost:11332)
|-457 rspamd: controller process (localhost:11334)
|-458 rspamd: normal process (localhost:11333)
`-459 rspamd: normal process (localhost:11333)
Jul 08 20:41:57 rainbow systemd[1]: Started rapid spam filtering system.
$ sudo systemctl start rspamd
Jul 08 20:53:07 rainbow sudo[434]: alarm : TTY=pts/0 ; PWD=/home/alarm ; USER=root ; COMMAND=/usr/bin/systemctl start rspamd
Jul 08 20:53:07 rainbow sudo[434]: pam_unix(sudo:session): session opened for user root by alarm(uid=0)
Jul 08 20:53:07 rainbow systemd[1]: Started rapid spam filtering system.
$ sudo systemctl status rspamd
* rspamd.service - rapid spam filtering system
Loaded: loaded (/usr/lib/systemd/system/rspamd.service; disabled; vendor preset: disabled)
Active: active (running) since Wed 2020-07-08 20:53:07 -03; 1min 50s ago
Docs: https://rspamd.com/doc/
Main PID: 437 (rspamd)
Tasks: 5 (limit: 4915)
CGroup: /system.slice/rspamd.service
|-437 rspamd: main process
|-438 rspamd: rspamd_proxy process (localhost:11332)
|-439 rspamd: controller process (localhost:11334)
|-440 rspamd: normal process (localhost:11333)
`-441 rspamd: normal process (localhost:11333)
Jul 08 20:53:07 rainbow systemd[1]: Started rapid spam filtering system.
