In general, HDDs are still superior over using SSDs for backups. Since backups tend to write numerous small files, they tend to "wear out" an SSDs memory cells. This is one reason that data centers use HDDs in general for this purpose. In addition, HDDs are still cheaper per GB than SSDs.
For example, the general rule for Time Machine backups is that the destination drive be, at least, 2-3x the storage space of the internal drive it is backing up. Depending on the Mac Studio model you have, it could be configured (AFAiK) to up to 16TBs. Trying finding a 32-48TB SSD without taking out a mortgage, even if they existed.
Finally, there is no real speed advantage of using a SSD over a HDD for backups.