There are certain esim providers that give you a number. Esimdb.com

Proton integrates directly with simplelogin. But you can use gmail for aliases with anonaddy or simplelogin, they just forward the alias emails to your real inbox.

It takes a little bit of effort but it’s a great time to do the following:

• get a password manager if you don’t have one already. I like 1password
• get an alias service. Proton bought simplelogin so it’s integrated, there’s also anonaddy
• gradually work through updating your online accounts from your old gmail to new aliases for each account (eg [email protected]) and set a complex password through your password manager that’s unique for each account

In a couple months you’ll eventually stop receiving emails to your gmail as you work through the accounts you use, and most incoming mail will all be through aliases. Then if you get spammed, you know what site leaked your email + you can turn off the alias and not get spam.