asciidoctor-pdf: Unicode characters ⌚☑💭📝🔒🔑⏰ work, but ↹⏎⇧ don't

Dear group,

for this problem, I've already checked, among others:
https://github.com/asciidoctor/asciidoctor-pdf/issues/1129
https://github.com/asciidoctor/asciidoctor-pdf/blob/v1.5.x/docs/theming-guide.adoc
https://discuss.asciidoctor.org/Troubleshoot-missing-glyphs-pdf-from-TOC-generation-td8585.html

but could not make any progress.
Using asciidoctor-pdf 1.6.0 on Ubuntu 20.04 LTS with this test file:

= Test
:experimental:    // for kbd:[F11] etc

[cols="1,12", frame=none, grid=rows]
|===
| ⌚      | watch
| ☑       | checkmark
| 💭      | think bubble
| 📝      | memo
| 🔒      | lock
| 🔑      | key
| ⏰      | alarm clock
| kbd:[↹] | ↹
| kbd:[⏎] | ⏎
| kbd:[⇧] | ⇧
|===

and this command line:

asciidoctor-pdf --verbose -a pdf-theme=default-with-fallback-font test.adoc --out-file test.pdf

the output is:

asciidoctor: WARNING: Could not locate the character `↹' in the following fonts: M+ 1mn, M+ 1p Fallback, Noto Emoji
asciidoctor: WARNING: Could not locate the character `⏎' in the following fonts: M+ 1mn, M+ 1p Fallback, Noto Emoji
asciidoctor: WARNING: Could not locate the character `⇧' in the following fonts: M+ 1mn, M+ 1p Fallback, Noto Emoji

And the resulting PDF has all symbols except the three ones mentioned in the warning messages.

Are these characters not included in any of the considered fonts?
How can I proceed to get ↹⏎⇧ into the pdf file?