Finally checked: TP-LINK TL-SM321B is supported by Turris 4.0.3:
dmesg | grep sfp
[ 5.282570] sfp sfp: module TP-LINK TL-SM321B rev 1.1 sn 35506106580385 dc 17-06-15
[ 5.291907] sfp sfp: LC connector, encoding 8b10b, nominal bitrate 1.3Gbps +0% -0%
[ 5.299674] sfp sfp: 1000BaseSX- 1000BaseLX+ 1000BaseCX- 1000BaseT- 100BaseTLX- 1000BaseFX- BaseBX10- BasePX-
[ 5.309788] sfp sfp: 10GBaseSR- 10GBaseLR- 10GBaseLRM- 10GBaseER-
[ 5.316072] sfp sfp: Wavelength 1310nm, fiber lengths:
[ 5.321397] sfp sfp: 9µm SM : 20000m
[ 5.325675] sfp sfp: 62.5µm MM OM1: unsupported/unspecified
[ 5.331436] sfp sfp: 50µm MM OM2: unsupported/unspecified
[ 5.337195] sfp sfp: 50µm MM OM3: unsupported/unspecified
[ 5.342956] sfp sfp: 50µm MM OM4: unsupported/unspecified
[ 5.348716] sfp sfp: Options: txdisable, txfault, los+
[ 5.354042] sfp sfp: Diagnostics:
I think it would be better to have armada-385-turris-omnia-sfp.dtb by default.