Hi theMcQ,
Welcome to the Apple Community.
Seems Safari needs more free space than your Mac now has free, after the update.
If so, with several tabs open Safari.could be struggling.
The Operating Service needs at least 50Gb free space. for smooth operation.
How to check, and /or free up storage space on your Mac.
https://support.apple.com/en-us/HT206996
If storage is not the issue
Sometimes the system struggles because third-party (non-Apple) apps are not optimised for the current software.
Activity monitor on your Mac is a handy way to see which apps are using all the energy:
https://support.apple.com/https://support.apple.com/en-au/HT202731
If that also, is not the issue, try this article :
If Safari on Mac doesn't open a webpage or isn’t working as expected:
https://support.apple.com/en-us/HT204098
Hope this helps :-)