The UI of Synth V is very small, however other applications like Firefox are displaying normally. Perhaps Synth V does not adapt to the screen 200% scale?
I found a workaround: Run Synthesizer V with command line argument:
./synthv-studio --with-scaling 2
Synth V now applies 200% scaling.
But I hope Synth V can apply scaling automatically according to display settings, or allow users to change UI scaling in the Settings panel.