If your portfolio spans across engine accounts, you can create a single Search Ads 360 bid strategy and apply it to all of the campaigns and other items in the portfolio. For example, you can create a "$10 CPA bid strategy" and apply it to your "Google - shoes" campaign in a Google Ads account and your "Microsoft - shoes" campaign in a Microsoft Advertising account.
All ad groups, keywords, and other targeting items inherit the campaign's bid strategy unless they override it explicitly. It isn't possible to apply a bid strategy to an engine account.
Search Ads 360 makes it easy to view all of an advertiser's campaigns on a single page. You can then use filters to view just the campaigns you're interested in, and then apply a bid strategy to all of the filtered campaigns -- even if the campaigns reside in different engine accounts. (You can do the same for ad groups, keywords, and product groups.)
While some types of bid strategy features are supported only by specific engine types, you can apply the bid strategy to multiple engines. The bid strategy will make the adjustments that are supported in the engine.
All campaigns and other items managed by a Search Ads 360 bid strategy are required to use the same currency. For example, if "Google Account A" uses the US dollar and "Google Account B" uses the Canadian dollar, you can't apply the same bid strategy to campaigns in both accounts.
When you create a bid strategy, you can select a currency. You can't apply a bid strategy to campaigns that use different currencies.