In theory, only one instance of Signal can be installed, under normal use. BUT, if you use a Work Profile in addition to the Main/Personal profile, you can run two instances of Signal, each tied to a different number. How do I know? I do so, using Shelter as the sequestering app (post here) on my dual-SIM phone.
I’ve also mentioned this over at the Signal user community, and, of course, on r/Signal, which this forum software will not let me link (two links max, even though I’ve been here for 2.5+ years now…).