I’ll quickly add a link to Lubuntu 18.04 LTS End of Life (30-April-2021) where I talked a little about using a EOL release (specifically Lubuntu 18.04 LTS in that case) but whilst still before EOSS (end of standard support which 18.04 is).
We don’t know what the final position of what 18.04 will be come EOSS, particularly with recent blogs from Canonical, but don’t forget to consider the past releases and what happened, ie. for some packages the upgrades came only if you converted the initially supplied deb packages with snap packages. ESM/UA/Pro support isn’t identical to Standard Support so be aware of those differences, with 18.04 EOSS April 2023.
ps & fyi: at this time my ibm thinkpad t43 used in example in 7th post on that thread still has 18.04 on it; but I expect that system will be replaced by Debian when EOSS is reached