We note that several of the "solutions" that you have tried involve compiling a driver for Realtek hardware. As we see from your lspci, your wireless driver is iwlwifi. You have an Intel wireless device, not a Realtek. Any driver you install for a Realtek device will be ineffective.
It is fairly common for new users of Ubuntu to read a forum post about solving a wireless issue and then blindly apply it to their system. They are usually disappointed when there is no improvement. While it is not dangerous to add a new wireless driver that your system doesn't even use, it is futile if you don't know what driver you have. I urge all Ubuntu users to determine what wireless driver they have before applying any fixes to the system. You can do so with the terminal command:
lspci -nnk | grep 0280 -A3
After determining, for example, that you are using the driver iwlwifi, if you are having difficulties, search only for answers applicable to iwlwifi, such as "slow wireless" iwlwifi or "connection drops" iwlwifi.
We also notice from your paste that you are running Network Manager and ConnMan. It is not surprising that you are getting confusing messages from Network Manager. It is telling you that it doesn't know what is happening as it is no longer in charge.
As ConnMan is really designed for embedded applications, Raspberry Pi, doorbells, routers, et al, and you appear to have an ordinary desktop installation, I suggest that you remove ConnMan. It is obviously not doing a good job for you.
sudo apt purge connman
Next, your resolv.conf file is faulty. Let's fix it:
sudo rm /etc/resolv.conf
ln -s /run/systemd/resolve/stub-resolv.conf /etc/resolv.conf
Reboot and let us hear the result. Do you connect and reach the internet?