Thank you for watching, voting, and commenting on this issue.
We use this data as well as many other inputs to feed into our prioritisation process. Having issues from other projects on a next-gen project/board will be something that will be available in next-gen, although it is not something that we will be focusing on in the next year. We want to share this with you to ensure you can plan out your use of projects within Jira Software effectively.
In the short term we recommend teams use classic projects when you need to include issues from multiple projects on a board. We apologise for the inconvenience this may cause you.
Please continue to vote and in particular please continue to add comments on how your teams find value when including issues from multiple projects on a board. This contextual information of what you are doing and why you are doing is invaluable for us in providing you with a product that will grow with your needs.