How to perform FullText search on numeric column in MySQL to meet user requirements
When searching for a numeric string in the middle, FULLTEXT is the wrong approach.  LIKE is the only approach, and it requires a full scan of the plates.  Live with it.

But... How often do you need to search for the middle of a string?  Not often.  If you have the left part of a string, LIKE '234%' works quite efficiently; it is a "range".  But then you need a regular INDEX, not FULLTEXT.

FULLTEXT is aimed at words, not substrings, not full strings.  Don't use it for licence plates.

Don't use INT for a plate number.  It is not a "number" on which you perform arithmetic; that is what the MySQL Doc is talking about.  The plate number is merely a string that often contains only digits, so use a VARCHAR with the minimal collation.  In the 'west', plates are numbers and capital letters.  So, COLLATION ascii_bin is optimal.  However, that means fold to upper case both the plate numbers as they are stored.  Also fold any query strings.  At the same time, remove any punctuation (dash, heart, star, etc) that is not actually important to the comparison.

I cannot address the collation specifics for Bangladesh, but I suspect that utf8_bin would suffice.