Bid strategy cannot be modified
If you’ve ever wanted to modify your bid strategy but couldn’t, there’s a reason.
This applies to target ROAS, cost-per-result targets, and bid caps. If you can’t edit it, it’s because you are using Advantage+ Campaign Budget (CBO). CBO is turned on by default even if you use a set of ads.
If you encounter this issue, please follow these steps…
how to fix it
When CBO is turned on, there will be a campaign bidding strategy.

This strategy will apply to all ad groups in the campaign. But you can set different goals for each ad group.

After you define your campaign bid strategy, return to your ad set. You can then edit the target.

This assumes you want to use CBO first. Another option is to use ad set budgets, where you’ll be able to edit the bid strategy and goals as normal.
i saw this coming
When Meta first launched the Advantage+ campaign, I noticed this change and wondered if it would cause confusion. Well, this issue came up in my private community recently, so that seems to be the case. I immediately realized the problem.