In Anvil, you have the ability to add to the <head> section of your page using Native Libraries. However, there is no option for me to change what is already there. Anvil automatically loads lots of js libraries by itself and sometimes I have no need for them so they just slow down my website.
Then there are also modals for Kerberos, SAML, Stripe, etc. which get picked up by Search Engines (So I see the snippet for online payment below my “free” community on Google.).
I know that editing that part can have serious consequences for someone who doesn’t understand what they are doing. This is why Anvil can provide proper warnings and also an option to reset all changes to ensure that nobody ends up messing their app.