Syracuse.com has a Bills UDFA Tracker going on.
https://www.syracuse.com/buffalo-bills/2021/05/buffalo-bills-udfa-tracker-who-did-team-sign-after-2021-nfl-draft.html
Tariq Thompson. S, San Diego State
The Bills added safety Tariq Thompson post-draft. Thompson had 210 total tackles, 11 career interceptions and 23 passes defensed in his collegiate career.
Syrus Tuitele, OL, Fresno State
The Bills’ first UDFA signing is Syrus Tuitele.
Fresno State announced the signing. Tuitele, 6-feet-6-inches tall and 318 pounds, had 26 starts at right tackle with the Bulldogs.