Problem with TableOfContents whith XeLaTex+ucharclasses+Babel

I want to write a greek-english text. I am using babel+XeLaTex. I have a problem with the table of contents: When these lines are included in my code

setDefaultTransitions{selectlanguage{english}}{selectlanguage{english}}
setTransitionTo{GreekAndCoptic}{selectlanguage{greek}} 

it produces the following error:

"LaTeX Error: Command rmfamily invalid in math mode. output.toc, line
67"

and a warning at the ‘ tableofcontents ‘ command, mentioning:

Package babel Warning: englishcontentsname not set. Please, define it after the language has been loaded (typically in the preamble) with something like: renewcommandenglishcontentsname{..} Reported on input line 23.

In the pdf, instead of ‘ Contents ‘ at the start of the ToC, it has ‘ ?contentsname? ‘

Here is the MWE:

documentclass[12pt]{extarticle}

usepackage{babel}
usepackage{ucharclasses}

babelprovide{greek,english}
babelfont{rm}[Ligatures={Common,Rare}, Scale=1.0]{Libertinus Serif}
babelfont{sf}[Ligatures={Common,Rare}]{Libertinus Sans}
babelfont{tt}{Libertinus Mono}

babelfont[Language=greek]{rm}{Kerkis}
babelfont[Language=greek]{sf}{Kerkis}
babelfont[Language=greek]{tt}{kerkis}

setDefaultTransitions{selectlanguage{english}}{selectlanguage{english}}
setTransitionTo{GreekAndCoptic}{selectlanguage{greek}} 

begin{document}
some text
blabla μπλαμπλα

newpage
tableofcontents
newpage

section{Introduction-Εισαγωγή}

subsection{test}

end{document}

documentclass[12pt]{extarticle}
usepackage{xcolor}
usepackage{fontspec}
newfontfamily{defaultfont}{Noto Serif}
newfontfamily{greekfont}{Kerkis}[Colour=blue]
usepackage[english,greek]{babel}
usepackage{ucharclasses}
setDefaultTransitions{defaultfont}{}
setTransitionsForGreek{greekfont}{}
%babelprovide{greek,english}
%babelfont{rm}[Ligatures={Common,Rare}, Scale=1.0]{Libertinus Serif}
%babelfont{sf}[Ligatures={Common,Rare}]{Libertinus Sans}
%babelfont{tt}{Libertinus Mono}
%
%babelfont[Language=greek]{rm}{Kerkis}
%babelfont[Language=greek]{sf}{Kerkis}
%babelfont[Language=greek]{tt}{kerkis}

%setDefaultTransitions{selectlanguage{english}}{selectlanguage{english}}
%setTransitionTo{GreekAndCoptic}{selectlanguage{greek}} 

begin{document}
some text
blabla μπλαμπλα

newpage
tableofcontents
newpage

section{Introduction-Εισαγωγή}

subsection{test}

end{document}