Using Ubuntu MATE 18.04 on two systems? I hope they're offline, or you have taken steps to keep your systems safe if those machines are used online.
That release was posted back in April 2021 as reaching End of Life - Ubuntu MATE 18.04 LTS reaches end of life
If you're stuck on that release, as you're using 32-bit x86 (i386), then I'll suggest moving to Debian GNU/Linux which still supported 32-bit x86; as Ubuntu now only provides specific packages in i386, and full support for 32-bit ARM (armhf); but ESM/Pro options exist for neither 32-bit architectures.
If you're using ESM, I hope you noted the actual terms of that support, as many packages are now only patched when they were converted from deb to snap package, as per 18.04 ESM docs (published prior to 18.04 reaching EOSS).