One of our members posted a document in the "Filed" section showing his upgrade procedure to a 3.2" screen @
/g/nanovna-users/files/Hardware%20Mods/NanoVNA%20new%203.2%20LCD%20display%20Herman%20ON1BES.pdf .
If you decide to go with a 2.8" replacement screen and have difficulty seeing the screen fonts then you might give hugen's 0.4.0AA firmware a try. It has a larger font size with the main penalty being only 4 memory storage locations instead of 5. See attachment for example display.
- Herb