That deck is so weathered, the only thing i think will buy some time is this. Its a solid coating, might fill in the roughness. I might use the textured finish.
https://www.homedepot.com/p/BEHR-Pr...and-Concrete-Coating-500505/308486758#overlay
https://www.homedepot.com/p/BEHR-Pr...and-Concrete-Coating-500505/308486758#overlay