Most of the functions in Microsoft Teams have a slightly different Keyboard Navigation method than most functionality within Canvas. Microsoft Teams will primarily use the Tab key to move between a group of objects, and then from that group, use the Arrow Keys to navigate within the controls of that group. However, if the focus indication is placed over a larger set rather than on a single control in a group, you will need to press the Enter/Return key first in order to interact with that group.
Example: Keyboard Navigation for a Message

Pressing the Tab key will create a focus box around the entire message

Pressing the Enter/Return key will place focus around the top half of the message

Pressing the Down arrow will move focus to the Reply section of the message

Pressing the Up arrow will move focus back up to the top half of the message

Message Top Half:
Pressing the Enter/Return key will display the Emoji Reactions, which can be selected with Arrows & Enter/Return key

Pressing the Tab key will move you to the “…” menu, which you can navigate with Arrows & Enter/Return key

Message Bottom Half:
Pressing the Enter/Return key will open the reply text field

Pressing Tab will place focus in lower settings and attachment menu bar

Pressing Tab again will place focus on the Send icon

Pressing Tab again will place your cursor in the text field

Hopefully this document helps give a good indication of how to navigate smoothly with the controls in Microsoft Teams. Additionally, Microsoft has extensive accessibility support documentation that includes screen reader walkthroughs & keyboard shortcuts.