How to Import MBOX to Gmail Mailbox without Thunderbird?

I am currently working on a crucial office project that requires the migration of approximately 20 GB of MBOX files into Gmail account. And, I also don’t want to lose any single data during migration.
Could you please provide recommendations or step-by-step instructions on the most straightforward approach to achieve this task? I am open to using professional tools or any other method that ensures a hassle-free import process.

You want to bring MBOX to Gmail without Thunderbird, so let’s try the most popular and powerful conversion tool named TustVare MBOX Converter Software. It is a demanding tool and one of the best tools compared to other software from the company. It is 100% safe for your device and free from any harmful viruses. It converts email from MBOX files to Gmail and 10+ formats. It offers a free trial version as the user understands it and downloads the software from TrustVare’s website.