I am a member of a PPU workspace (my account is on a separate Azure domain to the tenant, but with workspace admin rights), with the appropriate PPU license. However, on the 1st September, myself and all other non-admin members on my Azure domain have been forced to accept a Pro trial to access the content, despite all having PPU licences. The tenant has not changed the workspace requirements, as they all operate at PPU level as well.
Please check whether your PPU license expires .You can ask IT manager or the people with Global admin license or Billing admin license to check your license . If it has expired, go to the Microsoft 365 admin center to re-order.
The link below is to introduce the relationship and diff between PPU ,Pro and Premium per capacity .