The 4 KB SRAM (organized as 4K x 8) limits buffer-heavy applications like USB or large frame graphics; for I²C or SPI data logging it is adequate. If your compiled binary plus constant data exceeds 32 KB, step up to the 64 KB Flash variants in the same STM32F031 family (pin-compatible across the 28-pin UFQFPN package).
28-UFQFPN exposed pad — layout and thermal notes
The 0.5 mm pitch demands careful solder paste stencil design; a 0.25 mm aperture works for most assembly houses. Keep the decoupling capacitor (100 nF ceramic) within 2 mm of the VDD/VSS pair, and route the SWD signals (SWDIO, SWCLK) to a header for debug access.
ST lists the STM32F031G6U6TR as Active. The ROHS3 compliance covers current EU and China RoHS requirements. If you are dual-sourcing, the STM32F031G4U6TR (16 KB Flash) is a drop-in replacement with the same package and pinout — just a smaller Flash size.