Sometimes, search doesn't work as you expect in SharePoint (one example is multi-line text fields - and a list of crawled properties is at https://docs.microsoft.com/en-us/microsoftsearch/manage-search-schema). In particular with Lists, some column types aren't supported OOTB. But there is a way to get searching for all columns using managed properties.

The process is simple enough:

1. Setup a managed property for the column or columns you are not able to search on.
2. Re-generate the search index

Here's the process in a little more detail. You'll need at least Site Administrator access to complete these steps.

Setup a managed property

1. Go to the list of concern
2. Click Settings | Site Information | View all site settings
3. Click Search Schema (Under Site Collection Administration)
4. Click New Managed Property (just after the Filter box)
5. Enter details and note:
   1. Provide a logical name for the property
   2. Type is TextSelect Searchable, Queryable and Retrievable
   3. In the mappings box at the end of the form, click Add a mapping. Search on the field name in your list you are looking to search. For us, the field name was prefixed by ows_. You can map to more than one field - eg managed property date refers to all date columns
   4. Note that your column may not show up in crawled properties - and in many cases this is because there is no data in that field. Add a record with data in this offending field and then reindex. The column should now be available to select.
6. Click OK to save your managed property.

To reindex search

1. Go to Settings | Site Information | View all site settings
2. Click Search and Offline Availability (under Search)
3. Click Reindex site and confirm.
4. Wait a period of time for the reindex to complete (5mins for a small list)
5. More details at https://docs.microsoft.com/en-us/sharepoint/crawl-site-content

Custom date fields require a little extra work:

1. Update an existing RefinableDate property. Add an alias to make it easier (eg date) to search
2. More info at https://blog.velingeorgiev.com/how-set-datetime-managed-property-sharepoint-online

Notes on searching dates

You can use dates in format YYYY-MM-DD
Search in a date range eg 2022-01-01..2022-03-01
You can also use word terms as well:

• today
• yesterday
• this week
• this month
• last month
• this year
• last year
• But sadly… no “"last week”!

You can also use logical operators

• = Equals
• < Less than
• > Greater than
• <= Less than or equal to
• >= Greater than or equal to
• <> Not equal to

From https://techtrainingnotes.blogspot.com/2017/03/sharepoint-date-search-tips-sharepoint.html