What does it mean on my 2021 taxes "your return is still being processed"

Mine also changed to this today, Accepted on feb 15th and pending until this appeared today.

After the tax return has been Accepted by the IRS (meaning only that they received the return) it will be in the Processing mode until the tax refund has been Approved and then an Issue Date will be available on the IRS website.
See this IRS website for federal tax refund FAQ's - https://www.irs.gov/refunds/tax-season-refund-frequently-asked-questions

I spoke with a lady at the IRS yesterday and she stated “ they either need more time to process because they are back logged or I will get a letter in the mail with info” but she thought it was the first or the two scenarios and they are just very behind. She said to wait 4 days and check again or look for a letter in the mail. Not much help, but hopefully it’s just they are backlogged and I’ll have my return by the end of the week. Hope this helps some