Cross-Site Lookup filter

I have two sites. On Site 1, I have a list, that I used the LookupField to point to a list on Site 2.

The Lookup Field creates a value on Site 1/List 1 like {"id": 1, "text": "Title text of item"}

Now, I have a need to filter using pnp/js so I can find all items on List 1 with the ID from List 2

I tried to use

Web("").lists.getById("List1GUID").items.filter("List2LookupFieldname/Id eq 1").get().then((myres) => {

The query above fails, since List2LookupFieldname isn't a Lookup and does not have a /Id to query. So how do I query for all items in List 1 that have the Value of {"id": 1, "text": "Title text of item"}

Dear @sphilson,
The values are stored as plain text, so you can try using substringof filter instead - Use OData query operations in SharePoint REST requests | Microsoft Learn