Upgrade Photoshop 2020 to 2021 keep all settings, panel, plugins, brush and other ?

When you install a major Photoshop version. You can have Photoshop Migrate your presets. However, Third Party Plug-in are not migrated you need to install the plug-in you use into each major version of Photoshop you install. I do not install Lightroom so I not knowledge about it I know its does not support layered image files so I do not install it. I use Photoshop it uses the same Adobe RAW conversion engine as Lightroom.  ACR can use Lightroom raw conversion setting when Lightroom passes Photoshop a Camera RAW file it has made setting for. Howevet ACT UI differen from Lightroom RAW UI.  In Photoshop you can only use ACR UI Lightroom does not have a develop plug-in fot Photoshop. Photoshop can only use ACR for RAW conversion. Photoshop does not have its own RAW support.

The easy solution is to migrate as Ged says, but there is also an argument for not doing it. The thing is, preferences are prone to corruption over time because they are completely rewritten every time you quit the application. Errors accumulate. This is in contrast to program files that are read-only.

A corrupt prefs file can sometimes cause odd and unpredictable behavior. So it might not be a bad idea to start with a fresh prefs file every once in a while. Clean sheets.

Either way, save out your brushes and actions so that they can be easily reloaded. You do this from the panel fly-out menu.

Hi

I'd recommend backing up your settings before hand, Photoshop will give you the option to import your settings when updating but it doesn't always go according to plan

https://helpx.adobe.com/photoshop/using/preset-migration.html

You can also backup your preferences

https://helpx.adobe.com/photoshop/using/preferences.html

It's always a good idea to have a backup!

Can't answer for Lightroom as I don't use it

Edit: updating shouldn't affect the previous version settings