A 3-step plan was outlined for upgrading the version of jQuery bundled with core in June 2020.
The first step was included with WordPress 5.5, which stopped enabling jQuery Migrate version 1.x by default.
As part of #50564, part two of this process was committed, which updated the bundled jQuery version to 3.5.1. Alongside this, jQuery Migrate was also updated to the newer 3.3.1 version.
For the duration of WordPress 5.6, the migrate script will remain enabled by default, to capture any unexpected uses of deprecated features.
Do note that the Migrate script for version 3 is not compatible with features