You can config the shortcuts used by Spyder actions going to
Tools > Preferences > Keyboard shortcuts. I think
Shift + Enter is by default set for the
Run cell and advance action, but you could change that from the preferences and set it to be the shortcut for the
Run selection action. Also, just in case, some more info about the cell functionality mentioned is available at:
Editor — Spyder 5 documentation (spyder-ide.org)