Can I extend my 30-day upon arrival stamp for another 30 days in Thailand as a Russian citizen?

From October 1 2022 thru March 31 2023...

Entering Thailand now to October 1

Yes, your nationality DOES matter. When you attempt to enter Thailand without purchasing a visa prior to your travel,

You as a Russian entered Thailand for 30 days on a visa-waiver program that is not eligible for 30 days tourism extension. 6 countries including Russia are on the visa-waiver for 30 days. As you wrote, you can apply and get a 7-days-to-leave stamp if you apply for a tourism extension.

While, 52 nationalities enter Thailand for 30 days on the visa-exempt scheme that IS eligible for 30 days tourism extension.