Man pages matching name stapvars in section 3stap:

stapvars.3stap.en	debian 10 / systemtap-doc
stapvars.3stap.cs	debian 11 / systemtap-doc
stapvars.3stap.en	debian 11 / systemtap-doc
stapvars.3stap.cs	debian 12 / systemtap-doc
stapvars.3stap.en	debian 12 / systemtap-doc