Vou colar aqui a parte do php.ini em que aparece o mbstring, caso queira adicionar manualmente:
;;;;;;;;;;;;;;;;;;;;;;
; Dynamic Extensions ;
;;;;;;;;;;;;;;;;;;;;;;
; If you wish to have an extension loaded automatically, use the following
; syntax:
;
; extension=modulename
;
; For example:
;
; extension=mysqli
;
; When the extension library to load is not located in the default extension
; directory, You may specify an absolute path to the library file:
;
; extension=/path/to/extension/mysqli.so
;
; Note : The syntax used in previous PHP versions ('extension=<ext>.so' and
; 'extension='php_<ext>.dll') is supported for legacy reasons and may be
; deprecated in a future PHP major version. So, when it is possible, please
; move to the new ('extension=<ext>) syntax.
;
; Notes for Windows environments :
;
; - Many DLL files are located in the extensions/ (PHP 4) or ext/ (PHP 5+)
; extension folders as well as the separate PECL DLL download (PHP 5+).
; Be sure to appropriately set the extension_dir directive.
;
extension=bz2
extension=curl
;extension=dba
extension=com_dotnet
;extension=enchant
;extension=ffi
extension=fileinfo
;extension=ftp
extension=gd
extension=gettext
extension=gmp
extension=intl
extension=imap
extension=ldap
extension=mbstring
extension=exif ; Must be after mbstring as it depends on it
extension=mysqli
;extension=oci8_19 ; Use with Oracle Database 19 Instant Client
;extension=odbc
extension=openssl
;extension=pdo_firebird
extension=pdo_mysql
;extension=pdo_oci
;extension=pdo_odbc
;extension=pdo_pgsql
extension=pdo_sqlite
;extension=pgsql
;extension=phpdbg_webhelper
;extension=shmop
; The MIBS data available in the PHP distribution must be installed.
; See http://www.php.net/manual/en/snmp.installation.php
;extension=snmp
extension=soap
extension=sockets
;extension=sodium
extension=sqlite3
;extension=sysvshm
;extension=tidy
extension=xsl
;extension=zend_test
;;;;;;;;;;;;;;;;;;;
; Module Settings ;
;;;;;;;;;;;;;;;;;;;
