Here's one I've experienced. Suppose you have a table of customers, and you want to show an extra column of data on that page showing total orders, if and only if the viewer of that table has the manager role.
With an SPA, you'll be building an API (perhaps a 'REST' one, or GraphQL) to expose all the data required, such as customer name, email, etc, as well as the extra 'total orders' field iff they have the manager role. Now you need to make sure that either (a) that endpoint properly excludes that 'total orders' field if they lack the permission, or (b) you have a separate endpoint for fetching those kind of stats and lock that behind the role, or (c) (I hope not) you just fetch all orders then count them up! Now, having properly secured your API so that all and only the right users can get that data, you have extra logic in your front end such as 'if has role manager then show this column too'.
With a server side rendered page, you don't have to do the API security bit. You can just fetch all the data you like (often via a single SQL query), and then replicate the same extra logic of 'if has role manager then show this column too'. You've skipped the whole "make sure the API is secure" step.
Now suppose you want to add a dashboard for every admin user, not just managers, showing total orders system wide. Did you include that in your API already? Now you're likely going to need a new endpoint that allows any such user to fetch total system orders, while managers are still the only ones who can fetch per customer order totals. Having found a place to add that to your API, you can render it. With the server side page, there's no extra work to keep this secure. The dashboard is already restricted to the users who can see it, so just add the extra query to fetch total orders and display it.
In short, there's a whole layer that an SPA needs to secure for which there is no analogue with a server side rendered site. In an SPA you secure the API and then have the logic for what to show to whom. For the server side rendered site, you just have the logic for what to show to whom and that gives you the security for free.