my $clauses = join "|", map {quotemeta} @SearchTexts;
s{\b($clauses)\b}{<b>$1</b>}ig;
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• No need for the double matching.
• Use different delimiters if you have a slash in your replacement.
• No need to escape < or >.
• Don't use /o unless you're an expert (and then you won't).
• Don't use \1 in the replacement. That's what $1 is for.
• Eat more spinach.