Linux

GTX 580? Maybe you have to install an older driver, like the 470-series of the driver appears to support it: https://www.nvidia.com/en-us/drivers/unix/legacy-gpu/ Ubuntu has a bunch of older series of nvidia driver you can install for this purpose.

That would not explain your networking though. Unless that is also some older hardware too... But, a common thing to do as a new user in linux may be to find posts which answer "how do I install x in ubuntu" and they usually involve editing files under /etc/apt/sources.d/. This can wreck your system in this kind of way, so: have you done that? Or this is pure ubuntu, just regular apt update/upgrade and some apt installs?

The 580 drivers might just be the default for nvidia. I have two computers with nvidia GPUs that are like 10 years apart in age, but both look like they're running 580 drivers.

I don't really know what's wrong with the networking though. Maybe try updating from terminal if you haven't? sudo apt update && sudo apt upgrade

I have a feeling your gpu is too old for the latest Ubuntu version

I've been using Linux for years, but on my hardware I've never been able to get Ubuntu to work reliably. I now only use it when booting from a USB for backups, but even on a relatively recent Dell laptop with Intel graphics the GUI crashes constantly. IMO it isn't worth the trouble, but of course someone here will be oh-so offended by that.

After trying dozens of distros I went back to Mint because it just works.

Are you dual booting Ubuntu with Windows? Because Windows fast boot causes that behavior.

Welcome to Linux. We hope you enjoy your stay. That being said I'm wondering if It would work better in Debian. Linux Mint Debian Edition is basiclly a better Ubuntu. Ubuntu has weird bugs from what i've heard. I had a GTX series card and I always had problems with it. I had less issues on Arch based distros however. Maybe CachyOS or Garuda Linux might work better? Also, just a friendly warning Linux users like to argue with each other in the comments but it's just how we show our love for each other. As for things (wi-fi) working one day and then broken the next I only had happen on Ubuntu based distros. Do with that what you will. I hope someone else here has better advice. Best of luck and feel free to ask questions if you actually read my rambalings for some reason.

Your PC is too old for Ubuntus recent releases. Use a older distro like Debian.

On old hardware I use Debian. You can use whatever DE you prefer, I prefer x, but you have a graphics card so maybe you want gnome or kde. Ventoy liveusb with a few different distros can help you pick something that you like and let's you fully and quickly rage quit a distro if you come to realize that debugging legacy hardware/software compatibility issues is it's own hobby that is separate from not wanting to be tracked at the OS level or wearing sexy socks or whatever reason you have for using Linux.

You can boot Linux from a USB flash drive if your main installation isn't working. That might be better than searching for solutions from your phone. And a bootable USB flash drive is helpful when you can't boot from the internal drive. I always have one around, just in case, though I don't use it very often.

Booting from USB flash drive is a bit slow. A USB attached hard drive or SSD will be much faster or, if your internal drive is big enough, you can partition it to hold two Linux installations. Then, when one isn't working you can switch to the other with just a reboot, as long as it's not the boot loader that's broken.

I don't know which network manager Ubuntu uses, so I'm not sure whether this applies to you. I'm using Arch with the network manager systemd-networkd. I set it up manually from the CLI by creating a so called .network file in the /etc/systemd/network/ folder.

To "setup" and start using systemd-networkd, do sudo systemctl enable --now systemd-networkd.service. You will probably also need to setup systemd-resolved with sudo systemctl enable --now systemd-resolved.service because some services and/or programs need this for domain name resolution.

Then, check out point 3.5 on this page in the Arch Wiki: https://wiki.archlinux.org/title/Systemd-networkd

Use the section that applies to your setup depending on whether you are wired, wireless or both.

This of course assumes that Ubuntu doesn't use another network manager.

Maybe try a few distros on a live usb to see which work well with the hardware.

try a non wayland spin like fedora xfce https://fedoraproject.org/spins/xfce/download/

older machines get hiccups when they meet wayland