html, text and image widget doesn’t work anymore

hi to all,
after upgrading to 5.6 I found out that I can’t edit existing custom html, text, and image widget anymore, nor can I add a new one. On the frontend, anyway, everything looks as usual.

I Don’t get any console js error.

I’vre tried deactivating all plugins, and I’ve activated Twenty-Twenty-One theme, but problem persists.

All plugins and themes are updated.

When I try to edit widgets from theme customisation, widget areas in use aren’t detected at all: what I get is that i’m not using them, but I do.

Downgrading to 5.5.3 get all work again.

Could it be because of not having php 7.4 on my server? I’ve 7.3.26.