The list of problems is endless;
Rim and spoke failure, [this isn’t true] 😆
Stress cracking of head tubes, [neither is this] 😆 😆
Bottom bracket seizing, [and again this isn’t true] 😆 😆 😆
Excess pressure on rear tyre, [nope not true]:lol: 😆 😆 😆
Rear mech hanger failure, [nor this]:lol: 😆 😆 😆 😆
Hydraulic brake failure [interestingly (or not) there are naysayers who believe all brakes contain air and storing them vertically induces the air to move causing spongy brakes], I don’t believe this for one moment unless your brakes aren’t bled properly. 😆 😆 😆 😆 😆 😆
And the most dangerous issue is bumping your head when you store things under the bikes, which you will, I can speak from painful experience as all 3 of my bikes are wall mounted and hung by their front/rear wheels 😯
More seriously what I will suggest is a wall mounted security anchor and a big chain both gold standard; with the bike located as far back from the front door, out of prying eyes as possible. 🙁