Can I have multiple h1 paragraph styles but with different attributes?

Yes, Frans, PDF 2.0 does have the <Title> tag.

But PDF is not PDF/UA.

PDF 2.0 is the master "umbrella" PDF standard for all kinds of PDFs, including PDF/A (archival), PDF/E (engineering), PDF/X (print & graphic arts), PDF/UA (universal accessibility) and more subsets.  These subsets define how to use PDF for different purposes and uses.

Our future PDF/UA -2 subset standard will most likely define how to use the new <Title> tag, but that's not a given until the new standard is released and approved by the ISO.

Until it does, PDF/UA-1 is still the version that is in force today; therefore using the <Title> tag is not compliant with the current standard, and it won't do anyone any good because AT (assistive technologies) haven't been developed to recognize and process the <Title> tag, or anything else with PDF/UA-2.

Don't jump the gun on standards. If it's not in the current standard, don't use it. See https://www.iso.org/standard/64599.html about the ISO's statement re: review, "This standard was last reviewed and confirmed in 2020. Therefore this version remains current."

As @Jeffrey_Smith shows, you can have different formatting styles mapped to the same tag in the PDF.

For example, in my classes I show students that they might have a "regular" <H2> for subheads in the main story, but also might want the heading for a sidebar to have an <H2> in the PDF as well. They make 2 different formatting styles in InDesign, but map both of them to  <H2>.

I'm more concerned about how you're drawing your conclusions:

1. Headings in accessible documents denote the logical hierarchy of the document. Sometimes that jives with the visual appearance of the headings (example, bigger bolder with more white space is a higher level heading; smaller less bold with less white space is a lower level heading). But sometimes it doesn't. Nothing in the PDF/UA-1 standard says that heading levels must jive with their visual appearance.
2. Why are you designing the document with mutliple <H1> tags? The general interpretation of the PDF/UA-1 standard indicates that <H1> is the top-most level of heading...in other words, the Title of the document itself (or in large publications, the title of a major section, like a chapter of a book. Quoting the standard: "— If any heading tags are used, H1 shall be the first."

I'll be the first to admit that the PDF/UA-1 standard doesn't give clear enough direction on how to use heading tags or deal with the document's title. After all, there isn't a <Title> tag in the standard, so we can't use it in our PDFs. That leaves us with using <H1> for the title, which coordinates with traditional, pre-digital publishing standards (says this former hot-metal typesetter).

At this time  -- as PDF/UA-1 is the current standard  -- we recommend reserving <H1> for the document's title, and subsequent descending headings as <H2> through <H6> in a logical order. And PDF/UA-1 does not allow the skipping of heading levels: can't go from <H1> to <H3>, for example.

Remember, this is all interpretation of a murky part of the standard, so YMMV (your mileage may vary). All of us experts come up with our unique interpretations.

In a future version of the standard, PDF/UA-2, there might be some clarifications on titles and headings, but that version of the standard is in development and won't be available for a few more years.

—Bevi

(Delegate to the ISO committee for PDF/UA standards)

From the paragraph styles panel, select each style and export tagging, and map to H1