Short answer: YES.
You can choose your WAN port - 1 G E, 10 G E or SFP+.
It sounds like what you want is ATT 5G E --> Asus 10G E ---> Asus SFP+ ---> 10 E LAN Switch. It will work.
I have played around with with a similar config on my AX89 (Fios 1 G E --> Asus 10G E ---> Asus SFP+ ---> 10 E LAN Switch.)
BUT I only have a 1 Gig Fios connection so I don't know how close to 5 Gb true speed you will see from the 10G to the SFP+
On FIos with AI protection on, using the 1G or 10G E WAN port on the Asus , I took about a 5% hit to speed, getting about 920-950 Mbs up and down when Fios is at its best.
And to folks who ask "why do you need a 10 G home network?" I edit HD photos and 2k/4K video at home for fun and as a side gig. The files are massive and having 10G makes it much easier to move them on/off the NAS. Also, using fiber between floors for a home backbone just works.
I WISH i had 5 G internet. It would make it much easier to share files and work on multi user editting projects.