Most restaurants that focus on delivery are QSRs. While full service does deliver, usually, its not their main focus.
Within the QSR space, brands are mostly broken down by number of locations which influences their decision making with regard to their technology. Most established brands in Tier 1 markets do focus on technology heavily: its a significant revenue stream. However, their approach differs.
The McDs, Penera, Panda Express, Chipotle of the world usually stick to only one platform. The focus more on integration of Delivery, POS, and inventory more than covering significant amount of platforms. Some decide to use an off the shelf solution while others use a 3rd party delivery system on top of whatever their POS provider brings. There is significant complexity in this paragraph and they all approach it differently but the gist is the same.
Smaller brands that have ~1,000 locations or less begin to splinter into 2 groups: some focus on similar integration as above while others will support multiple platforms via several tablets. Since the revenue stream is significant, they focus on Ops to get everything in line and have gotten to be extremely good at managing/streamlining the process. Its not perfect but it works.
Brands between 20-500 locations will also manage multiple platforms but some invest into "aggregate" providers. Such companies will build out a unified backend for the location and integrate with multiple marketplaces (Grub, Door Dash, proprietary, etc.) to unify the system. Usually, they use a 3rd party for the admin that already has the infrastructure (OLO comes to mind). While in this approach streamlines operations, its quite costly as they charge for volume of orders.
Brands with less than 20 locations usually resort to just using 3-5 tablets on their walls for orders.
As a disclaimer, these are generalities and there are other factors that influence decision makers such as franchising percentages, Tier 1/2/3 markets, and their overall approach.
So to answer your question: most brands are currently moving to aggregate platforms or manage fewer platforms in order to streamline their operations. Large brands also use Yext to streamline their on-line marketing presence or other providers.