The floors where native fibre is not needed have a cheap ethernet media converter from fs.com, everything else (3 floor switches) are interconnected with 10Gbps SFP+ modules and 2.5G ethernet for the hosts.
All done thanks to the great https://michael.stapelberg.ch/posts/2020-08-09-fiber-link-ho...
(if you are reading this, I owe you several beers)