Installed Grafana plugins not visible

I have just installed Grafana on Ubuntu 20.04.2 LTS:

/var/lib/grafana/plugins# grafana-cli -v
Grafana CLI version 7.4.1
var/lib/grafana/plugins# grafana-server -v
Version 7.4.1 (commit: 07649d1313, branch: HEAD)

I tried to install some additional plugins following this arcticle:

Plugins folder looks like:
/var/lib/grafana/plugins# ls -la
total 16

drwxr-x— 4 grafana grafana 4096 helmi 19 23:19 .
drwxr-xr-x 4 grafana grafana 4096 helmi 21 20:24 …
drwxr-x— 2 grafana grafana 4096 helmi 19 21:17 ae3e-plotly-panel
drwxr-x— 4 grafana grafana 4096 helmi 18 09:43 grafana-piechart-panel

According to Grafana client plugins are installed OK:
/var/lib/grafana/plugins# grafana-cli plugins ls
installed plugins:
ae3e-plotly-panel @ 0.3.3
grafana-piechart-panel @ 1.6.1

Grafana logs says:
t=2021-02-21T20:26:43+0200 lvl=info msg=“Starting plugin search” logger=plugins
t=2021-02-21T20:26:44+0200 lvl=info msg=“Registering plugin” logger=plugins id=input
t=2021-02-21T20:26:44+0200 lvl=info msg=“Registering plugin” logger=plugins id=grafana-piechart-panel
t=2021-02-21T20:26:44+0200 lvl=info msg=“Registering plugin” logger=plugins id=ae3e-plotly-panel

I still cannot see these plugins in Grafana web ui:
http://192.168.NNN.NNN:3000/plugins

I been googling and rebooting the Grafana and Ubuntu several times. No luck.

Any idea how to troubleshoot and solve the problem?

I also modified grafana.ini-file:

allow_loading_unsigned_plugins = “ae3e-plotly-panel”

Still cannot see installed plugins.