I had the exact same problem with a WP update when I had a WP site, after several unsuccessful updates I gave up. A few days go by and I get a notification as admin the update was automatically installed on the server.
I remember seeing the same thing you show below, could not be verified as no signature was found I suggest waiting a few days, maybe a week to see if it updates on it’s own.
I read the knowledge base and updating with ftp. What I dont understand is why infinityfree does not complete the update/allow completion. On all sites at infinity free, it is indicating “There has been a critical error on your website. Please check your site admin email inbox for instructions.” Never an email in admin?
Updating WordPress is a complicated process which means that there is quite a risk of breaking stuff. There is a good reason why WordPress (and most other CMS) say that you should always make a backup before updating.
The strict limits on free hosting don’t help with this. Unfortunately, there is not much we can do about it. We can’t just increase the limits for all accounts, and there is no way to reliably detect software upgrades while reliably preventing such a whitelist from being abused.
Note that if you’ve installed your site through Softaculous, you can also use Softaculous to update your site, which should be more stable. Although it always takes a bit more time before new versions are available in Softaculous, so that’s not an option if you really can’t wait for another week to update.