I had the situation on a Pinephone Pro from this year where after doing the modemdistro upgrade I was getting up to to a slash through the telephone signal symbol on the GUI; it was still accepting the command to enter flash though.
I was not able to use ADB flashing nor some script flashing tools though because of permissions problems, while sudo ,command. or chmod'ing or chown'ing the script should work making myself root on the phone(mobian) was the only way to get them to run. I just started by creating a root shell, sudo su, and everything worked as advertised even if it didn't at first fix the modem function,
I was getting close to trying the pin-short option, which I dont think wouldhave done anything more than I already had, when I found the solution.
It still took scrolling in the git issues to discover someone linking the dev had a website with everything, even though it is not mentioned in the git anywhere.

To confuse issues further I had previously went through a round of trying to flash new ADSBs and themodemdistro firmware after the PPp arrived then tried flashing back to 'stock' when I had gotten the dysfunction issue, instead of trying toshort pads I left the phone overnight with no battery, and regained functionality when I booted in the morning.