USB-C Arduino Nanos? Well... I at Least Tried 

"Failure is optimal. It is a way to move forward and to try new things. We have this kind of false pressure on people that they need to succeed on the first try, and that shit is not real. It's okay to fail." - Thor Hall, Pirate Software. You tried, you failed, you learned, you'll do it better next time. Good on you man.

I liked how you showed your failures so that people can learn from it. I have also started working on SMD atmega8 board and made couple of versions. The first SMD soldering attempt was a huge disaster and the solder tin was all over the PCB. But after 2-3 boards I'm decent at it now. I also had to install minicore bootloader for atmega8 and I remember there was a DTR pin or something which had to be connected through a capacitor for the bootloading process to work. Will let you know after checking my schematics revisions

In theory the classic bootloader should work, according to the datasheet 328p code can run unmodified on 328pb chips. Only the device signature is different, if you enable verbose upload and just copy paste the avrdude commands in a terminal with an additional -F it should work. Once the original bootloader is installed the board should work as a nano in the IDE. As for flashing the bootloader that should work with the chip soldered in, else the idea of ISP (in system programming) is kinda pointless. I assume that something on your board is shorted sometimes, maybe excess solder or sth, that would explain the ftdi outages too. I’m by no means an expert but I just bought a few PBs cause they’re significantly cheaper and hand soldered them to .1mm copper wire

Your 100nF capacitor from DTR to RESET is what tripped you up. It's an Arduino-specific kludge to allow resetting the MCU through the serial port to invoke the bootloader when downloading - but it sabotages trying to wiggle the RESET pin quickly which is what's expected when you program an MCU with an external programmer. ALL in-circuit programmable MCUs warn you against placing ANY capacitors on the RESET line for this specific reason - it would screw up the fast transition needed. Also, 1K is a bit low for a RESET pull-up; it works fine during use, but depending on what your external programmer might have on the same line it might start interfering with a proper level on the pin when pulled low. 10K is fine and less intrusive.

Why not KiCad?

Why don't you use a stencil with solderpaste. Then put it on a cheap chinese heater plate and everything is perfect.

there is a clone called AR-NANOCH-UNS-TYPE-C and it is type-c

1 year ago I tried for the first time adding a usb-c to an esp32 but I wasn't sure how all these things work so I didn't even pass the schematics. Now after seeing this video I could give it another shot😀. Great video brother.

m8 do yourself a massive favour and get hot air soldering equipment and paste solder. The solder mask is called that because it repels solder. You hold your components in place. Spread paste across ALL the pins at once then give it the hot air. The solder automatically goes to the pins and pads and is repelled by the solder mask. Soldering the cpu takes about 30 seconds.

You need to make it 3.3 Volts too. 5V is outdated. UPDI programming is necessary too.

I guess your soldering station is crap, or your solder. Use solder flux