Is it possible to open a catalog an extenal hdd on ipad pro 2020?

DdeGannes is correct, but here’s more detail. Because although the iPad can do some of these things, it’s important to understand the difference between the capabilities of the iPad by itself, and the capabilities of Lightroom on iPad.

ragdesodanarg wrote:

Will I be able to import the photos from an SD to the external hard drive (just like I do on the pc)?

iOS 13 and later can import photos from a camera card directly to your choice of:

• Lightroom storage on the iPad, by importing through Lightroom.
• iPad internal storage, by importing through the Files app.
• External storage connected to an iPad, by importing through the Files app.

When you import to Lightroom from any of those three locations (camera card, iPad internal storage, iPad external storage), the photos are always copied from wherever they are into Lightroom storage on the iPad, then uploaded to Lightroom cloud storage as soon as possible when Internet is available, and removed from (but visible on) the iPad until you want to edit them. If you select a photo for editing, it is downloaded from the cloud and cached so you can work on it. This is different than how Lightroom Classic works on your PC, and a catalog is not involved.

Lightroom Classic and its catalogs, which use local storage as master photo storage, are different than the Lightroom (not Classic) cloud-based system on iOS, Android, Windows, and macOS.

If you import photos to an iPad, return to your PC, and open an Lightroom Classic catalog that is synced to Lightroom cloud storage, the imported photos are downloaded to your PC to a local storage location, and removed from cloud storage except for Smart Previews.

ragdesodanarg wrote:

Is Lightroom for ipad ready to open a catalog from an external hard drive?

Because of the differences above, Lightroom from iPad does not recognize a catalog from Lightroom Classic, because it uses the cloud as master photo storage, managed through the organizational tools in the Lightroom app for iOS.

I wish they had answered your question, not the question they thought you asked, but it looks like Lightroom for iPadOS doesn't see the LR catalogs on an external hard drive, or at least can't open them.  I'm irritated at this, since I have many catalogs organized, each for a particular shoot or location, and I seldom use collections, which is what Adobe seems to prefer.  Maybe in some future release they'll allow external hard drive catalog access, but I won't hold my breath.