Question about LXDE package for Ubuntu 20.04 - this package is newer than in bionic? Who is maintainer of the package?

You are misunderstanding how meta-packages work.

the package lxde is a metapackage which does not contain any functionality of its own, but it depends on certain other packages. This helps installing all packages that belong to the LXDE desktop environment easily, without the need to list them separately in an install command.

The list of dependent packages has nor changed between Ubuntu bionic and focal, and thus the lxde package did not change.

If you look at its details, you can see that lxde depends (among others) on (the current version of) gpicview, and the version of gpicview in bionic is 0.2.5-2 and in focal it is 0.2.5-3

Although lxde is identical in bionic and focal it causes different versions on other packages.

lxde is in the "universe" category and the standard support rules for "universe" apply.
The support for the lxde package itself, however, is rather irrelevant, because the real functionality is in other packages.

@Manfred Hampl, thank you for your professional answer :) Now I know that is metapackage but like we know each package "included" in metapackage are maintained by someone. So why for focal we don't have the latest version of packages? How I can find if these packages are still supported?

"So why for focal we don't have the latest version of packages?"

Which packages are you referring to?

And as general information why there aren't the most up-to-date versions of software in focal, please see
FAQ #3037: “no rolling release”.

For example:

- lxterminal for focal 0.3.2-1 but for hirsute we have 0.4.0-1build1
- pcmanfm for focal 1.3.1-1 but for hirsute we have 1.3.2-1

I know that LTS version have older software but if will be vulnerabilities maintainers will be fixed it? Or this software will be abandoned?

Did you read the FAQ that I linked in comment #3?
The fact that software versions are not updated to a higher version is not only true for LTS, but all Ubuntu releases.

I readed this. It is very logic that we don't have newer version of packages for system stability reason but I asked about security vulnerability. For example old packages from LXQt desktop environments are not supported by LXQt team (developers) so this mean that if security vulnerabilities will be found on LXQt 0.14.1 this means that only community will can fix it because LXQt Developers will not fix it because this is old release and we should use only the newest release but this release is not available on Ubuntu repository (for example LXQt 0.17). This is why I asked you. I asked about this LXQt developers and they told me about this problem and they suggested me contact with Ubuntu Community for example. So I must know how it is work when someone found security problem. If it is package from main I think it is not problem but when if it is from universe who will fix it if developers of package will not do this? This same problem can be with other universe packages so it is why I asked here. Community is community so Launchpad can be good direction to explain this problem.

"Community is community"

The "community" are the users of the software worldwide, including yourself.
You cannot expect that there is always somebody else who does everything.
Most things are done on best effort, as far as capacity allows.

I tested for example Fedora and LXQt is more light now than new version of LXDE. Maybe on focal it is better but Fedora have newer package of LXDE. So I must decide what desktop environment I will be use. LXQt work fine but I have problem probably with sddm and I can see a lot of artifacts on log in screen.

This subject is ended but I still didn't know how it is work on Ubuntu. I think that maintainer of the package is person from debian distribution which package is synced to Ubuntu repository? This means that packages of lxde environment like for example lxterminal doesn't have maintainer on ubuntu repository. This is simply copy of the package from debian? I know that you earlier wrote links with how it is work but my english is not superb and I didn't understand all of things are on these websites.

Thanks Manfred Hampl, that solved my question.