Phone bricked a few days after USBC replacement - potential solutions, repair, or junk?

The problem
I have a Fairphone 4 5g i have had for a long time and not always treated well (a screen replacement, 2 USB-C replacement, new back case and 2 protective cases later!)
The charging started to get dodgy, constantly buzzing charging, not charging, but would still charge in the same amount of time it was just annoying.
After 2 weeks of this I got round to changing the USB-C port which seemed to solve this, however a few power cycles later it suddenly died.
It has since been completely unresponsive, no sign of life plugged into any charger or whatever button combinations i press.
Troubleshooting already undertaken
i have taken out and replaced the port, i have taken the battery out and held the power button in for a few minutes and left it battery out overnight to fully discharge everything, then left it on to trickle charge from a low wattage non fast charge adapter

The Questions

  1. What is the potential problem? has anyone seen/ done this before?
  2. If it is as i suspect, that i somehow managed to do a static discharge into it during the last port swap (not impossible as i was in my gym kit when i did it and thats fairly staticy) what are my options, is this a terminal full mother board change out or is this something that can have a skilled person in a repair shop do a capacitor swap on. THe fairphone repair would be swap the motherboard and that would come to 350 in total, which isnt economic for me.
  3. I was intending on running this phone until it no longer supported the crucial apps i need (banking mainly) as i am not a ‘power user’ who needs the latest and greatest, but i am frequently clumsy so low cost and easy repairs are worth it. If the repairs are likely to be expensive as above, what is my next best option: Second hand like for like replacement at about 250euro, upgrade to a second hand fairphone 5 at probably 350 euro, or bite the bullet and spend double to get a new fairphone 6 and guarantee support for a few more years

while the battery was out? This would actually do nothing at all as far as I know.

So you tried different cable and charger I guess?

You might find a repair store that can check where the issue lies, i.e. checking Voltage etc.

Are you sure that your battery is okay?

The battery is fairly new and i had no problems with it before, but i think i have the old one somewhere that i can swap in and check
Yeah, ive tried a few chargers and a few cables that i know work with other devices.
Yeah i wasnt sure exactly what holding the power button in with the battery out would do, but some troubleshooting guides recommended that as a way of draining all the capacitors/ components and i thought id do every recommendation i could find before i came crawling to the forums to ask for help