users are actually already tagged if the full bech32 is used
nostr:nevent1qqszhs8y93mnj76va0wascdm0dt550e7683pqqdq5zh4fkw855w86wgpp4mhxue69uhkummn9ekx7mqzyzsq3hh327t0h2dq6matqn5064cgj2zanl2stkj6s0lg4t2h5dty6l6xc6n
but there should be away to select from a list when the @ symbol is typed.