How to fix an old iMac G4 1.0GHz-256MB-80HD?

It is a beautiful piece of art, and you ought to be able to play DVDs and CDs provided the optical drive is ok. If necessary, they can be replaced too, and they are not expensive.

Regarding disassembly and repair, that model is very easy compared to any later model. The optical drive is just above the hard disk drive, so once you get them out it's a simple matter of replace and reassemble.

You will need only a couple of commonly available tools. Arguably the most important consideration in your repair efforts will be that Mac's original installation media (grey discs) but if you don't have them then you will need a retail Mac OS X Tiger installation disc. It came in a black box with a big letter X on it. You will need it to install OS X on a new hard disk drive.

1.5 GB RAM is not a standard or supported configuration so if you run into trouble during installation you might need to revert that Mac to its original configuration.

ForteMente wrote:

3) I was able to connect to my WIFI network, and yet Safari is blocked

You do not mention the installed Mac operating system version (could be Mac OS X 10.2 Jaguar, 10.3 Panther, 10.4 Tiger, or 10.5 Leopard).

Anyway, browsers compatible with the above operating systems have difficulties with modern (secure, https) web pages. The few remaining plain http sites may work, though. See, for example, the following user tip by a brody for alternatives: Browsers by Mac operating system - Apple Community.

What should I do?

Eliminate existing keychain?

That's the way to fix it. A new Keychain will be created and set to = your login password, but you will need to repopulate it as requests for authentication appear.

(2) could "bit rot" that affects optical media as it ages. The fact you can read some, but not all, indicates the optical drive is probably ok. They also tend to fail with age — their laser diodes degrade and eventually become too weak to read or write reliably.

(A) and (B) are casualties of Internet progress. The overwhelming majority of websites will not work. The fact that Amazon.it works is a testament to their motivation for selling you stuff superior even to Apple.

Your Mac is very fixable, and the components you might need (hard disk drive and optical drive) are not expensive. If you should decide to do that yourself it's not particularly difficult either.

For the hard disk you will need an ATA hard disk drive (not SATA).

I can provide more information if you would like, but you asked "is it worth it?" and the answer is "it depends." What do you intend to do with that Mac? Even if you get it to work as well as it did when it was new, it will never be anything more than a pretty relic.

There was a (now discontinued) TenFourFox web browser for Mac OS X 10.4 Tiger. See also the aforementioned user tip. However, as indicated earlier, modern (secure, https) web pages do not work (well) with an old browser. With any compatible browser, you could go to a plain http page (for example, knubbelmac.de) just for a test, though.

Please note that some special procedures (intended for qualified personnel) are required when opening an iMac G4. If necessary, a web search for the exact model combined with words like disassembly, service, or repair should show you what to expect.

https://everymac.com/systems/apple/imac/specs/imac_1.0_17_fp.html

if it's such an old version of safari then likely it would not support much of the javascript stuff that newer websites rely on