@Dariusz Thanks for reaching here- Going through your query it seems the issue is resolved-
Update: Problem solved. You can close the question. It turned out I haven't enabled FCM V1 in Cloud messaging tab in Firebase
Glad that you were able to resolve your issue and I appreciate your effort in sharing the solution.
Your contribution will undoubtedly assist others facing similar challenges.
As the [Microsoft Q&A community follows a policy where the question author cannot accept their own answer] {https://learn.microsoft.com/en-us/answers/support/accept-answer} ,
I've reposted your solution. Feel free to consider "Accepting" the answer if you find it suitable.