Admin plugin is slow, nearly unusable

Hello,

I tried to install Grav (grav-admin-v1.7.42.3.zip) on Debian 11, PHP 7.3.
I didn’t install custom theme or plugins.
The server is isolated on a private network.

The admin of Gray is so slow, nearly unusable. It took like 1 min between each click on the right panel.
(Dashboard, Configuration, Accounts, ...) and same in tabs.

The server is not overloaded, he is running fine other software and wikis.

@benoitp, Please do not cross-post within 2 minutes apart, the same questions here and on Github.

In the end, people in one location is wasting their time and effort.

When not receiving an answer in one location after allowing it some time, you may consider posting in an other location. But please notify both parties about the cross-post and add a link on both sides.