Hi @Andrew Hohenkirk ,
Do you have any operations before this issue occurred?
To exclude the account issue, if you login in Teams using another PC (such as Win10), can you share screen normally?
In this case, we recommend you try to update the VM image by installing a new MSI as described in the Install or update the Teams desktop app on VDI section. You must uninstall the current version to update to a newer version.
Besides, if you’re migrating from Skype for Business on VDI to Teams on VDI. Screen share aren't currently supported in Teams VDI that are in Skype for Business VDI. For more details, you can learn it from:
https://learn.microsoft.com/en-us/microsoftteams/teams-for-vdi#migrate-from-skype-for-business-on-vdi-to-teams-on-vdi
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