Why did scripts and styles fly off in the WordPress admin panel?

Question

WordPress

Hello everyone, I have such a problem, I support one site, they have problems with optimization, I installed the clearfy plugin to set up all sorts of caches and so on at the minimum, but they had version wp 4.19, sort of, i.e. quite ancient.
Clearfy didn't want to work, told me to update the whole CMS to start working, I figured it out, downloaded the site archive from the host, dumped the database and updated this damn WP, now this is the problem: most plugins send me hello from the 90s, when there was no CSS yet came up with, i.e. styles and scripts do not work, although there are no 404 errors when connecting, i.e. Everything works, what's the problem?

This is how the same clearfy looks like, i.e. nothing works

Answer 1

1. A problem could occur during the update (something was not corny updated or updated, but not as described in the documentation). Also, classes (.class) or identifiers (#id) may have changed, but this has not been updated in CSS.
2. Try to roll back to clearfy installation. If nothing changes, then there may be a problem with the update.