You can also remove all the dots between the time values, by deleting the semicolon between the elements in the medium format section.
In Terminal, the following removes the name..
defaults write com.apple.screencapture name ""
In Terminal, this command changes to smaller filetype JPG..
defaults write com.apple.screencapture type JPG
So with System Preference changes and terminal commands, you get..
2023-05-05 at 153610.JPG
If you want to further "fix" the format to be only a numerical timestamp, you can select multiple screenshots in Finder, right click, select "Rename" and use Text replace dropdown to replace all dashes with nothing..
Just enter a single dash in the "Find" field and nothing the "Replace with" field.
Then you have..
20230505 at 153610.JPG
Run the multiple file Rename function with " at " in the replace field, and you end up with..
Otherwise, write a Finder script or use a third party rename app.