I am experiencing this problem as well. I attempted, as others, to follow the steps outlined above in order to correct the issue, but as others, the two diagonal arrows described in the support answer do not exist for me, nor does the option under "appearance and accessibility" to toggle the sidebar collapse on/off.
Perhaps if these issues could be remedied, or if you could inform us what version of Teams your support team is referring to, we could provide more details.
My system is owned by my organization, but these are the details I am able to provide at a glance:
Version information (copied from "About Teams")
You have Microsoft Teams version 24215.1007.3082.1590.You've got the latest version. It was last checked on 8/28/2024.The client version is 49/24080212008.
Windows information
Edition: Windows 11 Pro
Version: 23H2
Installed on: 3/28/2024
OS build: 22631.4037
Experience: Windows Feature Experience Pack 1000.22700.1027.0