i can see your struggling with this so i have to say, the easiest solution is to use another machine on your network as a "go between"
an osx Leopard 10.5 or 10.6 mac might be perfect for this purpose.. and you would just create an AFP share directory and simply drop files from one platform and pick it up on the other. you might have to share the same directory with SMB (Samba) for the newer mac to access it. so the server would be basically translating between the two protocols (AFP + SMB)
i personally use a PC setup with XigmaNAS which is a free file server running on BSD that supports net-a-talk
but theres alot to familiarize yourself with in setting that up but once u do its a beautiful solution with a mapped network drive on your old macs...
In OS X 10.8 Mountain Lion and earlier, AFP was the primary protocol for file services. Starting with OS X 10.9 Mavericks, Server Message Block (SMB) was made the primary file sharing protocol, with the ability to run an AFP server removed later in macOS 11 Big Sur.
another possibly easy alternative would be to simply install a net-a-talk server on your modern mac studio
https://netatalk.sourceforge.io/ if there is such a thing available i dont know i dont have a new M1/M2 mac as of yet
Netatalk is a Free and Open Source Apple Filing Protocol (AFP) fileserver. A macOS, Linux, BSD, or Solaris system running Netatalk is capable of serving files to many macOS (Mac OS X) and Classic Mac OS clients simultaneously.
that afterthought might be your best solution possible.