Ubuntu 18.04 LTS is now end of standard support.
If you are using a supported architecture you can have ESM or extended support options, however that is not all architectures and only includes a subset of the 64-bit architectures (no 32-bit; so no ARM32/armhf or x86/I386)
I still use i386 or 32-bit x86 hardware myself (mostly old IBM Thinkpads I really like), and have written about this on Lubuntu's discourse (as it's down I can't provide links to what I wrote there currently), but I wrote that I intended moving my own hardware to Debian; which I did a long time ago now. I outlined the reasons for the move prior to EOSS for 18.04 (2023-April).
I'm a Ubuntu member which means I get 50 machines I can extend LTS life using the ESM options, however that won't help a i386 machine.. which is why I jumped ship and went to Debian just after 18.04 EOSS for my last machine running 18.04.
Me, I'd recommend Debian. As for what release, that varies on your hardware & what you'll use your machine for. As I also do some QA of Debian releases too, I've found some of my hardware performed best (GPU or graphics/video hardware specific) on old-old-stable (10) rather than later releases (kernel mostly being the issue; not all GNU/Linux distributions have kernel stack choice as Ubuntu offers it); yet on other hardware it made no difference, thus I'd use stable (12) or old-stable (11) on those. In most cases my i386 hardware runs Debian 10 or 11 (ie. I vary version depending on my hardware; those running Debian 10 will upgrade in a few months to 11 which I've confirmed they'll run, just as they didn't perform as well running 11 I'll not move until I need to in June 2024)
FYI: If using a 32-bit ARM cpu; you can use later releases of Ubuntu & Ubuntu-MATE. Ubuntu 18.04 (18.10/19.04) were the end of the road only for 32-bit x86.