Leave this here for everyone who has a similar problem:
The RBAC API is considered unstable for now, see: Role-Based Access Control (RBAC) - Strapi Developer Docs.
I missed this the last time I’ve read the docs and it indicates there are changes coming!
My solution:
Changing the handler to be a function. It was at simple as that.
In my example:
const conditions = [
{
displayName: "Filter-Company-A",
name: "filter-company-a",
handler: {
"Company.Name": { $eq: "CompanyA" },
},
},
];
becomes
const conditions = [
{
displayName: "Filter-Company-A",
name: "filter-company-a",
handler() {
return { "Company.Name": { $eq: "CompanyA" } };
},
},
];
In my tests the handler property has to be a function no matter what value the query aims for (nested or not nested). This surely will be fixed in an upcoming release. Gonna have a look into that making an PR for the docs later if there isn’t already one.