@laren3 There is a table for estimating your One Repetition Maximum lift, without ever lifting anything that heavy, if you scroll down in the link below. The key is to start small and build up slowly with guidance. It usually takes months to get to the 80-85% of 1RM used in the LIFTMOR trials and ONERO.

The amount of weight that you can lift about 8 times in a row, but not 9 times, is about 81% of your 1RM. You do not have to lift it 8 times to test this, you can lift 5 times then ask yourself if you could possibly lift that thing 4 more times in good form. If yes, then you would add weight. If you could only lift it only one more time then you would need to remove weight.
https://strengthlevel.com/one-rep-max-calculator