Full Reset iMac 2014 running macOS 10.9.5 Mavericks

..Micrart Group..

A iMac 2014 'build year model' could run up to macOS Big Sur 11.x

[Mavericks? ~ Not likely a ceiling for any shipped as-new in 2014.]

macOS Catalina is compatible with these computers - Apple Support

//support.apple.com/en-us/HT210222

Most older Mac OS have an need for 'web browser' upgrade; before

the actual system itself shows failure to work online. Firefox, Brave;

and a few others continued to allow secure access; at this time none

would suffice to provide security online, none would run in Mavericks.

How to download macOS - Apple Support

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

Software upgrades for older-to-newer macOS hardware could

be matched from Apple support's article "how to download".

32-bit app compatibility with macOS High Sierra 10.13.4 and later -Apple Support

//support.apple.com/en-us/HT208436

Certain macOS / OS X versions had been dropped; some old

model systems, may have seen feature upgrades. If so, those

may have support article details indicating their need.

(If there should be need, one might be able to re-install 10.9.5

on the hardware it originally shipped with. That might still work

for offline tasks, and/or project specific third-party software.)

• iMac (Retina 5K, 27-inch, Late 2014)

Model Identifier: iMac15,1

Part Number: MF886xx/A

Latest compatible operating system: macOS Big Sur

Tech Specs: iMac (Retina 5K, 27-inch, Late 2014)

User Guide: iMac (Retina 5K, 27-inch, Late 2014)

• iMac (21.5-inch, Mid 2014)

Model Identifier: iMac14,4

Part Number: MF883xx/A, MG022xx/A

Latest compatible operating system: macOS Big Sur

Tech Specs: iMac (21.5-inch, Mid 2014)

User Guide: iMac (21.5-inch, Mid 2014)

Identify your iMac model - Apple Support

//support.apple.com/en-us/HT201634

If you've done nothing else to the El Capitan, to start in Safe

mode could help; at least to get past that restart issue..

How to use safe mode on your Mac - Apple Support

//support.apple.com/en-us/HT201262

Extra links in the above could help to install/reinstall an

other macOS version, help find & use recovery versions

among other small details that could make or break this.

Once you've upgraded to El Capitan, an idea which may

work better, might be to try for High Sierra 10.13.6; as

that might give the hardware a patch for firmware; but

you may just erase and install a higher macOS instead.

Mojave 10.14.6 is a fairly good one; and link to get download

is from the same page others were located. Be sure to get

installer downloads with Safari browser; instructions indicate.

My Late 2012 Mac mini quad-core server, has two rotational

hard disk drives; those are a known bottleneck too. At least

one of them should be upgraded to solid state drive. Present

those have two partitions, in each as well. (Has four macOS.)

(You could consider starting up from Internet Recovery; and

then use the internal recovery to erase the El Capitan. If you

like; from the Recovery partition; start with Option Key held.

..And be sure to 'back track, on exiting' each item used there.

Sometimes this works well; other times, not so much.)

I'm a bit rusty on these things; have to admit. Had given

older Macs away; in working order. Still have G4 Mac mini

Late 2005 w/ 10.5.8 (& tenfourfox last stable version).. And

mid 2012 MacBook Pro 2.5GHz core-duo with Mojave, on

a smaller 240GB SSD (third party, has Flash, no HDD.)

So I have done some maintenance, boot from Internet Recovery

and occasionally run that version Disk Utility to check & repair

drives, etc. With later MacOS, these new Systems create more

nested internal partitions; and these have their own rules, too!

Perhaps you may choose to ask a new question, as a 'marked as

solved question' may deter others from reading your newest one.

This could help get additional attention; also look into Mac OS

systems communities, once you choose ideal macOS version

as final destination; those areas have upgrade topics, beyond

that are inclusive of hardware limitations. (HW limits upgrade.)

Some active newer users have a dogpile of evidence of their

credible worth. Whereas my participation has been less active

from an initial start, in 05/2003; the original 'Apple Discussions'

is long gone; several topic histories have vaporized too.

..To say my offline life is rather overwhelmed in the

present time, would be an understatement, as well.