I have gmail on my MacBook Pro, pop-ups saying "keychain 'login' can't be found.

The Keychain password may be reset or made a new.

Changes to the user account ~ makes older ones fail.

You may actually need to be sure your Mac has Backup

(time machine on external USB HDD) and reinstall macOS

maybe from macOS Recovery. I'd answered other question

and then saw underlying issue is contributory.

• About macOS Recovery on Intel-based Mac computers - Apple Support

https://support.apple.com/en-us/HT201314

Restore from Time Machine: Restore your files from a Time Machine backup.

Reinstall macOS: Download and reinstall the Mac operating system.

Disk Utility: Use Disk Utility to repair your disk or erase your disk or other storage device.

[About 'the last thing you could' try, is make &

use a bootable installer to reinstall macOS.]

^ not the first thing.

• If you forgot your Mac login password - Apple Support

https://support.apple.com/en-us/HT202860

• Forgot (admin user) Password - Apple Community (reply)

https://discussions.apple.com/thread/252670909?answerId=255029985022#255029985022

• If your Mac keeps asking for the keychain password - Apple Support

https://support.apple.com/en-us/HT201609

• Keychain Access User Guide (Table of Contents) - Apple Support

https://support.apple.com/guide/keychain-access/toc

• How to Create a New Keychain on Mac | osxdaily

https://osxdaily.com/2020/07/25/how-to-create-a-new-keychain-on-mac/

Firstly you really need to make several good backups, these take time.

These use external USB hard drives attached to Mac by wire, and run

automatically each hour; should be 4TB capacity. These are lower end

insomuch as these need not be super-fast SSD.

The USB connected hard drive enclosures stay connected to Mac. Some

of my older desktop Macs, or portable Macs, get attached to backups

at least once a month, this takes more time to catch-up & backup.

My under-utilized Macs also have their own USB-powered backup drives.

[And takes hours to make first-time "Time Machine" backups from scratch.]

Articles on "how to" are available as instructions on Apple support site.

I've uploaded their web page links a few times each year, to this site.

Examples from other sources include this third party site's content:

• Easy Redundant Mac Backups with Time Machine and Multiple Drives | osxdaily

https://osxdaily.com/2013/08/09/time-machine-multiple-drives-mac/

• How To Setup and Use macOS and OS X Time Machine [Guide] - AppleToolBox

https://appletoolbox.com/how-to-setup-and-use-osx-time-machine-guide/

• Back up your Mac with Time Machine - Apple Support

https://support.apple.com/en-us/HT201250

(others are saved in bookmarks/browser in mac mini i7)

..before this site logs-out automatically, time to post..

This is job-one. Backups you can restore any content you want.

So when internal drives fail, you could rebuild a system offline.

Certain content, saved, would need their product keys saved too.

The idea of dragging items to make backup copies

may work OK for simple documents; Time Machine

is already in the macOS & can backup well enough.

El Capitan is a little outdated, browser options, few

and no security update in awhile; yet depending on

what macOS MacBook Pro has; 10.11.6 is old.

Instructions for Time Machine are covered in earlier post.

You need to have at least one 2TB or 4TB USB backup

drive, one that simply is port-powered from USB port

on the Mac. May take 3-6 hours to save first backup.

• How to get old versions of mac OS - Apple Support

https://support.apple.com/en-us/HT211683

The versions in above linked page, are in two sections.

First shows later macOS (newest download installers)

and Second tells of older macOS, uses different path

to upgrade later macOS. Mojave 10.14.6 is last macOS

that can use 32-bit & 64-bit s/w. If upgraded no further

there shouldn't be an issue with 'software/drivers'.

(Sometimes outdated systems need a newer version

before going to latest one the hardware could support,)

As far as email and other stuff, at least two good separate

backups, Time Machine and clones; can be helpful. Those

loose-ends would normally be saved with the backups.

For other levels of complexity, external drives with

their own power supply, can be used to make Clones

[Which also may be useful to run the Mac externally.]

Low-cost clone utilities such as 'Carbon Copy Cloner'

(bombich) or 'Super Duper' (shirtpocket) may be OK.

Took awhile to get back to this thread. Been busy

now, snow's starting to melt and temps going up.

And other details are piling up to keep me busy..!