Timing is everything. You flash GApps before your first boot into the OS. If you boot into LineageOS first and then try to install GApps, you will likely encounter constant "Setup Wizard has stopped" crashes.
Move your chosen GApps zip file to your SD card or internal storage. Recovery: Boot your phone into Lineage Recovery or TWRP. gapps for lineage os 191 top
Includes a "Debloater" function; offers frequent updates. Timing is everything