You can use a 18mm band with:
Fossil Q Tailor
Fossil Q Tailor Gen 3 Venture/Gen4 Venture/Venture HR for LG Watch Style
Withings Activate
Withings Stell HR 36mm
You can use a 20mm band with:
Galaxy Watch Active 2 (40mm & 44mm)
Galaxy Watch Active (40mm)
Galaxy Watch (42mm)
Galaxy Watch3 (41mm)
Galaxy Watch4 Classic (42mm & 46 mm)
Galaxy Watch4 (40mm & 44mm)
Galaxy Watch5 (40mm)
Galaxy Watch6 (46mm)
You can use a 22mm band with:
Galaxy Watch3 (45mm)
Galaxy Watch (46mm)
Gear S3 Frontier
Gear S3 Classic
Fossil Q Explorist HR Gen 4
Fossil Gen 5
Fossil Men’s Gen 5 Carlyle HR
Fossil Women’s Gen 5 Julianna HR