Hello @Arjen Krap
Are you using a work account in your Microsoft 365 tenant or a free account (personal)?
If you are using a work account, you need to check the coexistence mode (also known as upgrade modes) of your Teams user.
Teams have 5 upgrade modes: Islands, Skype for Business only, Skype for Business with Teams collaboration, Skype for Business with Teams collaboration and meetings and Teams only.
If your user is in the "Skype for Business with Teams collaboration" or "Skype for Business with Teams collaboration and meetings" mode, you will have limited features in your Teams client.
In the first mode, you will be able to use Teams only for group collaboration (channels). In the second mode, you will be able to use Teams only for group collaboration (channels) and Teams meetings.
Please make sure your user is in "Islands" or "TeamsOnly" mode to have the full list of features available.