What options do I have to upgrade an unsupported i386 version of Ubuntu to an operating system with newer packages?

I am trying to upgrade Ubuntu 18.04 to 21.04 (i386 architecture) on a Dell laptop in order to be able to install proton VPN.

Output message:

There will not be any further Ubuntu releases 
for this system's 'i386' architecture. Updates for 
Ubuntu 18.04 LTS will continue until April 2023.

Are there any options to upgrade perhaps to another newer Linux platform that would support a GTK version that would be compatible with Proton VPN or is my only option to upgrade my hard disk?

First check if your CPU is really 32 bit. You may be running a 32 bit version of Ubuntu in a 64 bit CPU, and then you can install a 64 bit version of Ubuntu on this.

Run the command lscpu and look for CPU op-mode(s):. If the output is 32 bit, 64 bit, you can fresh install a recent, 64 bit version of Ubuntu/Xubuntu/Lubuntu on this computer (the last two need less resources). If it is 32 bit, head on to the next part of the answer.

Ubuntu does not support i386 architecture (which is 32 bit) beyond version 19.04. If you want to continue using a recent operating system with updated packages, you will have to migrate to a different operating system. You have several options.

1. Debian i386 -- Debian is very similar to Ubuntu. You can install the LXDE or XFCE desktop environments, which are lightweight.
2. Q4OS -- Debian based OS, optimized for older computers. The Trinity desktop environment (actively maintained fork of KDE 3.5) requires only 128 MB RAM, and is super fast.
3. MX Linux -- Debian based distro tailored for old computers.
4. Arch Linux 32 -- Hard to install, but can be made extremely lightweight, and it hosts the latest version of packages in its repositories.
5. Tiny Core -- Extremely light weight operating system, which works on systems with 48 MB RAM or greater.

Note: None of these operating systems are supported on this site.

You will need to sign up for ESM in order to install a 32-bit Ubuntu release with a x86 CPU since all 32-bit versions are now outside of community support.

Unfortunately, ESM releases do not receive community support, including here on Ask Ubuntu. For this device, you might want to look for another Linux distribution outside of Ubuntu if you want community support and/or don't want to use ESM.

As 32-bit only hardware is quite old now, fewer and fewer operating systems are supporting it, including Ubuntu. Debian still has 32-bit releases and is similar to Ubuntu, since Ubuntu is actually based on Debian.