Happy Monday @Masanori_Misawa and thank you for your patience!
I got an update from the team who has confirmed that from April 1st, Asana will no longer support Internet Explorer. You can learn more about it here: Deprecating Support for Internet Explorer (IE11) Notification? - #3 by Marie
I understand your customers use IE but for to ensure the best experience with Asana I would highly recommend using any of the official compatible browser listed here: Asana supported browsers and troubleshooting steps | Product guide • Asana Product Guide
I’m closing this Bug now since this issue will not longer be prioritised. Sincere apologies for any inconvenience this might have caused you and please let me know if there is anything else I can help you with or if you have any follow-up question!
Have a great week @Masanori_Misawa!