SUMMARY
The current Konsole zoom level should be remembered between sessions.

STEPS TO REPRODUCE
1. Run Konsole
2. Change the "zoom" level (actually I think this changes the font size) a few steps by using ctrl+- or ctrl+=
3. Quit Konsole
4. Run Konsole again

OBSERVED RESULT
The previous zoom level (font size) is still in place.

EXPECTED RESULT
The default zoom level (font size) is back in place.

SOFTWARE/OS VERSIONS
Operating System: openSUSE Tumbleweed 20230427
KDE Plasma Version: 5.27.4
KDE Frameworks Version: 5.105.0
Qt Version: 5.15.9
Kernel Version: 6.2.12-1-default (64-bit)
Graphics Platform: X11
Processors: 4 × Intel® Core™ i5-7200U CPU @ 2.50GHz
Memory: 15.5 GiB of RAM
Graphics Processor: Mesa Intel® HD Graphics 620
Manufacturer: HP
Product Name: HP ProBook 450 G4

ADDITIONAL INFORMATION
Remembering the zoom level is, I think, an expected behaviour, just as windows remember their size and position (or maximise state). For example, Dolphin, Firefox, VS Code/Codium, behave like this.

It is possible to change the font size in Konsole to a different number to change the default, but this requires cloning the default profile and changing the setting in there, which is quite a lot of steps and not very discoverable. Plus, this isn't entirely a workaround, as it only changes the default, doesn't fix the "remember the previous setting" issue.