Beginning with the 2021 releases, Internet Explorer (IE) v11 will no longer be supported by SugarCRM solutions. This includes the next releases for Sugar Sell/Serve/Market.
The Sugar 10.3 release is the last Cloud release and Sugar 10.0.x is the last on-prem release that will support IE v11. SugarCRM is asking that users move off IE v11 as soon as possible to avoid any service disruptions.
Microsoft's announcement to end support for IE v11 on August 17, 2021, can be found here.