There are multiple issues with the Markup Toolbar post update to iPadOS17.x - the two most significant being:
1) Any pre-existing saved Signatures cannot be accessed subsequent to the iPadOS 17.x update. Signatures are stored within your Apple Keychain; signatures pre-existing this update are still accessible from devices running iPadOS 16.x or earlier.
2) The markup Magnifier tool is similarly absent from iPadOS 17.x - despite this function still being documented as available within the updated iPad User Guide.
Absence of these tools affects both Notes drawing and system-wide markup tools.
You might also be well advised to seek assistance directly from from Apple Support - as they may wish to record and escalate as appropriate. You can contact the Support Team using the Support link at top-right or bottom-left of this page. Alternatively, you can initiate and manage your support cases from Apple devices using the excellent Apple Support App. If not already installed, the App can be downloaded from the App Store:
https://apps.apple.com/app/apple-support/id1130498044
Apple invite submission of comments and bug reports via its Product Feedback portal. For iPad and iPadOS:
Feedback - iPad - Apple
When submitting a Bug Report (recommended), ensure that you include details of your iPad model and installed version of iPadOS within the body-text of your report. Don't rely upon the pick-list - as this rarely includes the current versions. Every report counts; unless sufficient reports are received, Apple might not assign resources to investigate and resolve the issue.