Can't create a filter on joined table

[Thomassso]

Describe the bug
Report goal: create product list and sold product quantity total and product quantity sold with discount.
I couldn't create filter (filter on order.discount column) on joined table.

To Reproduce
Steps to reproduce the behavior:

1. Create a new Custom question
2. Coose Products as main table
3. Left join the Orders table
4. Try to add filter after the join. Column: order.discount . Filter operator: greater. Filtered value: 0 .
5. The Add filter button is always inactive, you can't finish the filter creation.

Expected behavior
The Add filter button will be active when everything is set in filter creation window.

Screenshots

Information about your Metabase Installation:

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    "java.version": "1.8.0_262",
    "java.vm.name": "OpenJDK 64-Bit Server VM",
    "java.vm.version": "25.262-b10",
    "os.name": "Linux",
    "os.version": "4.15.0-133-generic",
    "user.language": "en",
    "user.timezone": "GMT"
  },
  "metabase-info": {
    "databases": [
      "postgres",
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    ],
    "hosting-env": "unknown",
    "application-database": "h2",
    "application-database-details": {
      "database": {
        "name": "H2",
        "version": "1.4.197 (2018-03-18)"
      },
      "jdbc-driver": {
        "name": "H2 JDBC Driver",
        "version": "1.4.197 (2018-03-18)"
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    "run-mode": "prod",
    "version": {
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      "date": "2021-04-06",
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      "hash": "471eda1"
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Severity
Our employees need to filter data based on various categories. Some of categories are in other tables. We use star schema. Joins are present in most of our reports.

Additional context

[flamber]

This seems to apply only for number types - I can filter string and date types, and PK/FK numbers.
And doesn't matter if implicit/explicit - and is in Simple and Notebook

[alxnddr]

Fixed by #15605