Best Albert alternative for global search
It seems that Albert is still maintained, a new version was released recently: https://github.com/albertlauncher/albert/
ulauncher
The best alternative in my opinion is ulauncher.
It's discussed to include it as a standard app in Debian and maybe ubuntu will follow. The ulauncher homepage gives many plenty of extension and also how to build your own extension. It is highly configurable and works with plasma (baloo, ...) and gnome.
For installing follow the description on ulauncher download section , where a deb or PPA installation links are given.
For the ppa use:
sudo add-apt-repository ppa:agornostal/ulauncher
sudo apt update
sudo apt install ulauncher
To run it as a service using systemctl
you may copy the following script into your service directory:
$ sudo editor /lib/systemd/system/ulauncher.service
[Unit]
Description=Linux Application Launcher
Documentation=https://ulauncher.io/
After=display-manager.service
[Service]
Type=simple
Restart=always
RestartSec=1
ExecStart=/usr/bin/ulauncher --hide-window
[Install]
WantedBy=graphical.target
Now you can start or enable ulauncher as service.