I don't think the Proton developers are on lemmy, this community is maintained by enthusiasts and users. You might want to reach out to them directly.
Proton
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
Proton VPN is the world’s only open-source, publicly audited, unlimited and free VPN. Swiss-based, no-ads, and no-logs.
Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
We (reddit mods) usually read everything here, and closely work with the rest of the Proton Support and Social Teams. But we can understand that Proton is not interested (as of now) to modify their icons. So the previous answer remains.
Someone posted about this over on Reddit. This was Proton’s response:
Hello, the launcher icons are part of our design system and need to come from our Design team. Thank you for the suggestion and the understanding.