Anytime to different products come together (same as changes in plane) you would silicone and not grout, grout would always crack, not if, but when. The two materials expand and contract differently leading to the grout cracking.

Thank you! Do you think it would work to have some grout to match foyer and a thin bead of silicone at joint?

No. Grout Color matched caulk, backer rod beneath it if necessary.

Mapei (and maybe others) has a line of sanded caulks. I have this same problem at two doorways.

Scrape out all of the grout and fill the joint with sanded caulk. If it's a deep gap you can use a backer rod or a different colored caulk to build it up, then use the matching sanded caulk on top.

https://www.mapei.com/us/en-us/products-and-solutions/products/detail/keracaulk-s

Thank you!