We map the extraplanar gas, with $\sim$50─200 pc resolution, in nine star-forming galaxies using Multi-Unit Spectroscopic Explorer (MUSE) observations from the GECKOS VLT Large Programme targeting edge-on galaxies with similar stellar mass as the Milky Way. The narrow range in stellar mass ($\pm 0.35$ dex) of the GECKOS sample makes it ideal for studying trends with star formation rate (SFR). We find strong extraplanar emission reaching $\sim$2-8 kpc from the disc mid-plane in all targets with $\rm {SFR}\ge$1 M$_{\odot }$ yr$^{-1}$. Targets with SFR $\, \ge \,$ 5 M$_{\odot }$ yr$^{-1}$ have brighter, more extended H$\alpha$ emission compared to lower SFR targets. In high-SFR systems, the gas velocity dispersion ($\sigma _{\rm H\alpha }$) shows a biconical morphology, consistent with the expectation of outflows. This agrees with previous works suggesting high velocity dispersion in a biconical shape is a good means to identify outflows. We find mixed results using line diagnostics ([O III]$_{5007}$/H $\beta$─[N II]/H $\alpha$ and $\sigma _{\rm H\alpha }$─[S II]/H $\alpha$) to spatially resolve ionization mechanisms across the extraplanar gas. The highest [N II]/H $\alpha$ are found in the extraplanar gas of the highest SFR systems, yet main-sequence galaxies have the highest [O III]/H $\beta$. While the morphology of [N II]/H $\alpha$ may be useful to identify outflows, the absolute value of the line ratio alone may not distinguish strong outflows from extraplanar gas of main-sequence galaxies. The ubiquitous extraplanar emission can be interpreted as the result of feedback, in the form of large-scale winds for starbursts or smaller-scale galactic fountains for main-sequence galaxies. Moreover, shock-heating may ionise gas at the interface of the disc and the circumgalactic medium, independent of the source of the gas.