How to Bold Specific Column Values in Power BI Table Visual.

Your Target column have numbers and texts, thats why its say's cannot convert text to int.
Now i update the measure to include texts, please try it:

BoldTarget = 
VAR RawText = SELECTEDVALUE(financials[Country])
RETURN
    IF (
        ISBLANK(RawText),
        BLANK(),
        VAR LengthOfText = LEN(RawText)
        VAR Chars =
            ADDCOLUMNS (
                GENERATESERIES(1, LengthOfText, 1),
                "@Char", MID(RawText, [Value], 1),
                "@Code", UNICODE(MID(RawText, [Value], 1)),
                "@BoldChar",
                    SWITCH (
                        TRUE(),
                        // Digits 0–9 → 𝟬–𝟵
                        UNICODE(MID(RawText, [Value], 1)) >= UNICODE("0") &&
                        UNICODE(MID(RawText, [Value], 1)) <= UNICODE("9"),
                            UNICHAR(UNICODE("𝟬") + UNICODE(MID(RawText, [Value], 1)) - UNICODE("0")),

                        // Uppercase A–Z → 𝗔–𝗭
                        UNICODE(MID(RawText, [Value], 1)) >= UNICODE("A") &&
                        UNICODE(MID(RawText, [Value], 1)) <= UNICODE("Z"),
                            UNICHAR(UNICODE("𝗔") + UNICODE(MID(RawText, [Value], 1)) - UNICODE("A")),

                        // Lowercase a–z → 𝗮–𝘇
                        UNICODE(MID(RawText, [Value], 1)) >= UNICODE("a") &&
                        UNICODE(MID(RawText, [Value], 1)) <= UNICODE("z"),
                            UNICHAR(UNICODE("𝗮") + UNICODE(MID(RawText, [Value], 1)) - UNICODE("a")),

                        // Percent sign
                        MID(RawText, [Value], 1) = "%", "％",

                        // Dot
                        MID(RawText, [Value], 1) = ".", "·",

                        // Hyphen
                        MID(RawText, [Value], 1) = "-", "－",

                        // Default: keep original
                        MID(RawText, [Value], 1)
                    )
            )
        RETURN
            CONCATENATEX (
                Chars,
                [@BoldChar],
                "",
                [Value],
                ASC
            )
    )

Just assign your value to RawText  variable, but make sure that is correctly formatted.

Thank you