1. The last firmware version was. 2.0.2, however the Canon EOS 20D is 20 years old and is well out of its support life - there will be no service support if it has a problem, and Canon sites no longer offer the firmware updates for it.
To be honest, I would not waste your money updating lenses for that camera. If you have an R7, then invest in RF or RF-S lenses (RF is for full frame and will work on the R7 APS-C camera body, RF-S will work only on APS-C bodies). Because you cannot use RF or RF-S lenses on DSLRs like the 20D, if you want to be able to share, then get a R-series body.
FWIW: Canon EF vs EF-S Lenses - Differences Explained - Photography Pursuits. The same principle applies to RF glass: i.e. RF lenses are designed for Full-frame cameras, while RF-S lenses are designed for APS-C cameras, like your R7. FF bodies will not work well with RF-S lenses, even though they will physically connect.
Since you have an R7 and you want to have compatibility, you could get either a FF R body like one of the R6 versions, or an R8 (which is also good), and use the RF and EF lenses with that - those bodies have the better focus and tracking compared to the R7. Alternatively, consider another R7, or an R10 which will work with all the lenses you have but will not have IBIS or such a big battery.
You can look for bargains for cameras on the Canon Refurb site: these may be new but over-stock, opened but not used, demo or display units - good as new with a Canon warranty. For a general walk-around lens, for a Full-frame the RF 24-240 lens is brilliant (I have one) see: Shop Canon Refurbished RF24-240mm F4-6.3 IS USM | Canon U.S.A., Inc. and
for the APS-C platform the RF-S 18-150 is a good walk-around unit. If you want another telephoto lens, then consider the RF 100-400 which is good and fairly cheap Shop Canon Refurbished RF100-400mm F5.6-8 IS USM | Canon U.S.A., Inc..
If you want to splurge, the RF 100-500L is a deadly lens but not cheap - Shop Canon Refurbished RF100-500mm F4.5-7.1 L IS USM | Canon U.S.A., I.
If, despite all this, you want a lens for the 20D, don't get the 75-300 - they are arguably Canon's worst optic. Instead get the Shop Canon Refurbished EF 70-300mm f/4-5.6 IS II USM | Canon U.S.A.: it will work with your R body via a Canon EF-RF adapter, so can still be shared and is a great optic. That said, my advice as to the futility of investing in a body that is not compatible with your R7 still stands.
cheers, TREVOR
The mark of good photographer is less what they hold in their hand, it's more what they hold in their head;
"All the variety, all the charm, all the beauty of life is made up of light and shadow", Leo Tolstoy;
"Skill in photography is acquired by practice and not by purchase" Percy W. Harris
