This is common if you have remnants of other Adobe versions. Download the Adobe Creative Cloud Cleaner Tool from the official Adobe site to wipe old files before trying again.
macOS 10.11 (El Capitan), 10.12 (Sierra), or 10.13 (High Sierra). adobe-illustrator-cc-2018-v22-1-0-312-macosx-2-2gb-2022
If prompted to sign in or buy, select the "Trial" or "Install" option. This is common if you have remnants of other Adobe versions