Hello @ChristofferUlvestav-2699
Welcome to Microsoft Q&A Platform,
Route tables on Bastion subnet are not supported:
https://learn.microsoft.com/en-us/azure/bastion/bastion-faq#udr
Best regards,
----------
Please don’t forget to "Accept the answer" and “up-vote” wherever the information provided helps you, this can be beneficial to other community members.