Using fonts from the LaTeX Font Catalogue.

[Bob Tennent]

 >|BrushScriptX-Italic is also known to TeX as "pbsi8t". 
 >|A quick search using Voidtools 'Everything' reveals
 >|that TeX Live 2021 contains, in addition to the
 >|aforementioned, t1pbsi.fd, pbsi.sty, pbsi8t.vf,
 >|pbsi8t.tfm, pbsi8r.tfm, pbsi.tfm, pbsi.map and
 >|config.pbsi.  Strangely, it does /not/ contain
 >|"t1pbsi.sty", wherein Boris found a reference to
 >|"pbsi.fd", and indeed my entire 32TB disc farm does
 >|not contain a file of that name, nor does it contain
 >|Boris' "pbsi.fd".  Perhaps these are specific to Unix
 >|installations ??? I wot not.

kpsewhich should tell you that these files are located as
follows:

  texmf-dist/tex/latex/brushscr/pbsi.sty
  texmf-dist/tex/latex/brushscr/t1pbsi.fd

Bob T.