I tried the latest master branch containing that PR but it can't seem to sign the lowest possible 0.1sat/vB transaction at first.
But after manually adding 1sat to the absolute fee, it let me sign the transaction.
How exactly did you get the server to accept and sign your transaction?
I used Electrum master branch's
latest source code where the mentioned pull request was merged
And then launched it via Python (
after setting up the dependencies and requirements).
After that, I just connected to the mentioned server that accepts 100sat/vKb transaction fee and it went quite smoothly.
BTW, signing part is done via client where the wallet that contains the private key are saved, the server isn't involved in it.