This question already has an answer here:
Xubuntu 19.04 and Lubuntu 19.04 (smaller distros) says: "There is not enough drive space. At least 8 GB is required"
Is there a previous version of any of those distros that can work with the USB space I have?
1) Someone said my question may already have an answer here: Can I install Ubuntu on a 3.5GB mini PC?
That answer was written in 2013. It refers to Lubuntu 13.10 which is rather old. Better answers with more recent versions should be available and tested nowadays. Thank you.
[The accepted answer to that question was updated to 2019 Ubuntu versions before you posted the edit before this one. I suggest that you take some time to read it, specifically list item 4] <-- I didn-t write this. I reviewed the post above and there's nothing there written in 2019.
2) Someone said my question may already have an answer here: How do I install Ubuntu to a USB key? (without using Startup Disk Creator)
Nothing to do with my problem about the USB space I have.