Lubuntu 18.04 LTS is end-of-life with regards Lubuntu.
I’ll refer you to
I’ll suggest you run ubuntu-support-status and you can see which packages are common with Ubuntu 18.04 LTS (which uses the GNOME desktop & comes with 5 years of supported life; meaning it’s supported till 2023-April), and those which aren’t supported.
If you look in the second link you’ll see me make mention of ubuntu-support-status, using an old IBM Thinkpad t43 on which I still use Ubuntu 18.04 LTS (with LXDE) or what was Lubuntu 18.04 LTS (it’s i386 only so whilst it was capable of running 18.10 & 19.04; they are fully-EOL so it runs 18.04 with partial support). With that machine; my alternative is Debian (which I know it runs, I used it in QA-testing of Debian Buster & Bullseye) but given how I use that box I’ve not felt a need to switch.
FYI: I’ll now move this thread from Support to Off-topic as 18.04 is EOL & is not a Lubuntu Support issue.