いつも通りxamppを起動して、ApacheとMySQLのstartボタンを押したらMySQLだけ起動しなくなった。
OS：Windows 10 Pro 21H2
XAMPP：7.4.29
次の手順で復旧できましたが対応後のXampp環境に問題があるかもしれません。
あくまで自己責任でお願いします。
私の場合、Xamppは開発環境で使っているため問題があればXAMPPを再インストールしる予定です。
復旧できた手順と、MySQLが起動しなかったときのログは以下の通りです。
復旧手順（念のためにxamppフォルダをバックアップしてください）
- xamppを停止する
- xampp > mysql > backup フォルダに移動し、ibdata1ファイル以外をすべてコピーします
- xampp > mysql > data フォルダに移動し、２でコピーしたファイルを上書きで張り付けます
- xamppを起動する
MySQLが起動しなかったときのログは以下の通り
Xampp Control Panelのログの内容（xampp-control.log）
9:36:30 [main] Initializing Control Panel
9:36:30 [main] Windows Version: Enterprise 64-bit
9:36:30 [main] XAMPP Version: 7.4.29
9:36:30 [main] Control Panel Version: 3.3.0 [ Compiled: Apr 6th 2021 ]
9:36:30 [main] Running with Administrator rights – good!
9:36:30 [main] XAMPP Installation Directory: “c:\xampp\”
9:36:30 [main] Checking for prerequisites
9:36:30 [main] All prerequisites found
9:36:30 [main] Initializing Modules
9:36:30 [main] Starting Check-Timer
9:36:30 [main] Control Panel Ready
9:36:37 [Apache] Attempting to start Apache app…
9:36:37 [Apache] Status change detected: running
9:36:46 [mysql] Attempting to start MySQL app…
9:36:46 [mysql] Status change detected: running
9:36:49 [mysql] Status change detected: stopped
9:36:49 [mysql] Error: MySQL shutdown unexpectedly.
9:36:49 [mysql] This may be due to a blocked port, missing dependencies,
9:36:49 [mysql] improper privileges, a crash, or a shutdown by another method.
9:36:49 [mysql] Press the Logs button to view error logs and check
9:36:49 [mysql] the Windows Event Viewer for more clues
9:36:49 [mysql] If you need more help, copy and post this
9:36:49 [mysql] entire log window on the forums
mysql_error.logの内容
2022-09-18 9:36:47 0 [Note] InnoDB: Mutexes and rw_locks use Windows interlocked functions
2022-09-18 9:36:47 0 [Note] InnoDB: Uses event mutexes
2022-09-18 9:36:47 0 [Note] InnoDB: Compressed tables use zlib 1.2.11
2022-09-18 9:36:47 0 [Note] InnoDB: Number of pools: 1
2022-09-18 9:36:47 0 [Note] InnoDB: Using SSE2 crc32 instructions
2022-09-18 9:36:47 0 [Note] InnoDB: Initializing buffer pool, total size = 16M, instances = 1, chunk size = 16M
2022-09-18 9:36:47 0 [Note] InnoDB: Completed initialization of buffer pool
2022-09-18 9:36:47 0 [Note] InnoDB: 128 out of 128 rollback segments are active.
2022-09-18 9:36:47 0 [Note] InnoDB: Creating shared tablespace for temporary tables
2022-09-18 9:36:47 0 [Note] InnoDB: Setting file ‘C:\xampp\mysql\data\ibtmp1’ size to 12 MB. Physically writing the file full; Please wait …
2022-09-18 9:36:47 0 [Note] InnoDB: File ‘C:\xampp\mysql\data\ibtmp1’ size is now 12 MB.
2022-09-18 9:36:47 0 [Note] InnoDB: Waiting for purge to start
2022-09-18 9:36:47 0 [Note] InnoDB: 10.4.24 started; log sequence number 650543269; transaction id 646431
2022-09-18 9:36:47 0 [Note] InnoDB: Loading buffer pool(s) from C:\xampp\mysql\data\ib_buffer_pool
2022-09-18 9:36:47 0 [Note] Plugin ‘FEEDBACK’ is disabled.
2022-09-18 9:36:47 0 [Note] Server socket created on IP: ‘::’.
参考にさせて頂いたサイト
Error in starting MYSQL in XAMPP
以上です。