Standing up a toy sidekiq + rails environment for experiments and for tiny projects is a 10 minute operation. Standing one up for large projects, taking care of deployment without breaks, restarting sidekiq without losing jobs, scaling the environment in reaction to traffic, etc. is a lot more work.

Also standing up sidekiq requires managing your backend storage. If you have time and skills for that, great. Otherwise, a managed service may be better.

On top of that, you need to actually deal with system maintenance for all of those components normally. Any managed solution (whether that's serverless, or effectively-close-to-serverless like heroku) may be a good idea.