Please check the following if your fields are not available/visible in Salesforce Report Filter

1. Make sure the Field Level Security is set so that it is visible to the Users for selection.

2. Check the Field Accessibility. Open the Field in Salesforce Setup. Click the “View Field Accessibility” button to confirm it is set the Users Profiles.

3. Go to “Rename Tabs and Labels” in Salesforce Setup. Make sure the Field label is not overridden. If it is overridden, then use the new label used.

4. If the Field is from a Managed Package, go to Override in Salesforce setup. Msure the Field label is not overridden as part of it. If it is overridden, then use the new label used in the Override.

5. Check the following for additional limitations.

https://help.salesforce.com/s/articleView?id=sf.notes_on_entering_filter_criteria.htm&type=5