/
\%(^\|\s\)
\@<=\%(:\)
\%(\%([^:'[:space:]]\+\)\%(:\)\)*
AppendixR
\%(\%(:\)\%([^:'[:space:]]\+\)\)*
\%(:\)
\%(\s\|$\)
\@=
/

vimwiki#tags#search_tags generates a Vim regex based on g:vimwiki_tag_format and vimwiki#vars#get_syntaxlocal('tag_format').

/
\%(^\|\s\)
\@<=\%(\W#\w\@=\)
\%(\%([^#:[:space:]]\+\)\%([#[:space:]]\+\)\)*
AppendixR
\%(\%([#[:space:]]\+\)\%([^#:[:space:]]\+\)\)*
\%(\)
\%(\s\|$\)
\@=
/

Modify the preceding for compatibility with ripgrep pcre2 regex syntax.

(^|\s)(?<=(\W#\w))(?=(([^#:[:space:]]+)([#[:space:]]+)))*

 #EnergyNorthwest #PFSS #AppendixR #GNF3 #TRACG-LOCA #EPU
 #AppendixR