The QGIS All Releases page hosts older installers. Look for files ending in x86.msi or x86.exe (indicating 32-bit) rather than x64 .
Modern 64-bit systems are now standard, and only about 7% of users were on 32-bit systems when support was dropped in late 2020. To find the last compatible versions, use these sources: qgis 32 bits download
All releases since version 3.20 only ship with 64-bit executables. Important Installation Tips How to reinstall QGIS 2.18 as qgs-ltr - GIS StackExchange The QGIS All Releases page hosts older installers