Also, I tried to just copy the plugin folder into corresponding folder in file system (like we do with FTP).
And WordPress was supposed to find and list the plugin, but it didn’t.
Some weird behavior: I was able to install generateblocks.1.8.2.zip (654KB) several times, but can’t install generatepress.3.3.1.zip (1038KB).
So can it be that something is not allowing the upload depending on file size? But I think I checked the php settings, the size of uploaded file is more than 10 Mb…
So a theme should be uploaded from Themes page, plugins should be uploaded from Plugins page.
I tried to do everything from Plugins page and themes uploading was failing…