Things are slowly starting to get better in a lot of the fields I interface with.

Payroll and accounting software? Many great browser-based offerings. Unfortunately that also means the backend is running in the developer’s servers, but these applications were generally proprietary to begin with.

EMR company I’ve done a lot of work with (used to be an engineer there), has essentially halted progress on their Windows-only native client (and it was DEEPLY entrenched in Windows) and is now browser based, retaining 99% of functionality. This one always connected to a proprietary backend anyway.

Own a VW, Audi, Seat, Škoda, Bentley or Lamborghini (depending on model year for some of those)? The popular 3rd party diagnostic software for those, called VCDS, now has a mobile variant if you buy the wireless dongle instead of the cable - it runs a server in the dongle itself that you connect to via wifi, and it displays the sofware as a website. Of course it’s available for non-mobile browsers too.