The previous admin probably knew what you don’t: there were changes to WP since 5.3 that might not be compatible with some of the plugins you have.
WP 5.5, 5.6,and 5.7 all made changes to jQuery. The symptoms you describe sound like plugin or theme JS that is failing, causing core scripts to not be run.
There is a plugin to help with this, temporarily, called Enable jQuery Migrate Helper.
If that doesn’t solve it all, you can use Health Check plugin in Troubleshoot mode to disable plugins for your user only, to isolate the problem.
Ok, I found the culprit plugin.
I could agree with you, Joy, regarding the fact they could know something I do not. However, I do know they are not ethical, they do not respond to their client, they loose control over the website, and all that after being paid in full for an incomplete job.
After doing some research, I found that:
– The theme they picked (without consulting the client) uses a premium plugin for visual composing the pages – WP Bakery Page Builder. Suspicious.
– The theme shipped with a strange plugin called ThemeFTC that does not have a detail link in the plugins list, and each and every link associated to the plugin redirect to a maintenance and non-secure page. Again, suspicious.
If I disable this ThemeFTC plugin, the plugin search issue is gone, but the site looses some functionality like the basic click to open pages and products. Instead, a faded background appears (like the ones when cookie notices pop up) but no dialog appears. Need to press ESC key and stay in the same page.
Also, I have been trying to search for the plugin responsible for the cookie notice since the current one seems broken (it was already broken before I started to update plugins and WordPress itself).
Bottom line: we will remodel the site and apply a new theme. Old theme and associated plugins are trash. Seems the culprits are the ones who developped the theme and that ThemeFTC plugin, since they are nowere to be found and that plugin does not have a detailed window with information about it.
The WP Bakery builder is a popular plugin (not hosted here), so not that suspicious.
In the WP admin, the plugin link for View Details is only available for plugins from the WP repository, so that is not suspicious, although the author can put other links in there or in the readme file.
Feel free to share your experience in a review of any plugin or theme that is hosted here. For those that are not, well, if the free part is hosted here and it has an upsell, the paid version is fair game in a review.
I deactivated all problematic plugins and I managed so successfully search and install new plugins.
When that seemed right, I got the same symptom now. With all plugins deactivated except WooCommerce, it runs ok, I can install themes and search for plugins.
If I activate one or another plugin I know they are ok (I have them installed in my other sites), I just can’t search for plugins again. And if I try to install any theme, the spinning instalation icon stays like that forever.
I assume the issue is not with the plugins now, since I have them installed in other sites without issues. Now everything is updated. I installed the jQuery Migrate Helper plugin but seems it can’t help in anyway. At least I don’t see logs after trying these procedures with annoying results.
What can it be now?
The symptoms point to JS not running, and that happens when a script dies (takes down all other scripts).
Monitor the JS console during the action that is problematic.