question

If this is a DIY battery, adjust the cell limits on the BMS, the inverter will still report 100% (it is a relative metric) but you will be using less of the pack.

If this is a commercial battery, don't bother, they have already taken care of this for you in the design and configuration. This is an internet myth born from buying cheap EVE cells with unrealistic charge/discharge profiles.

This are Victron Batteries and MG Batteries how you limit the Charge off Quattro or Multiplus charge to max of SOC 50% by the Grip?

I think you have a Smart battery Setup, so that is why your very low for 12V Lithium packs, voltage settings are being ignored. You are most likely in "External Control" mode.

I have not found a way to only charge to 80% SOC, and it is not a good idea to do that anyway.

If the Battery has a BMS (depending on the specific BMS) it will most likely do cell balancing, and it usually only does that once the battery is at or near 100% charge.

SOC calculations in the BMS or Smartshunt, BMV712 etc.. drift over time, and in many cases they rely on a 100% charge (triggered by the charge rate having dropped to a small percentage of the Bulk rate) to reset the calculated SOC to 100%.

What damages Lithium batteries is spending lots of time at elevated voltages.
If your battery has a built in BMS that is communicating with the GX and/or Multi ie. "External Control" the BMS will take care of that itself, as it overrides any charging voltages that you set on the MultiPlus. (Will still use the maximum charge current that you set on the Multi)

What I do on Non Smart Lithium Batteries is:
Set the Float Voltage lower, (as Low as I can, but taking into account that if I go to low, Bulk charging will not trigger reliably, as it only triggers once the Battery voltage has fallen 0.2V under Float. (0.2v for 12v system, 0.8V for 48V system, when battery type set to Lithium in Ve.Config)
(13.5 V is a good place to start) - See your Battery Specs.

I also set the Absorption Time to one hour or two hours.
The higher you set the Absorb Voltage, the longer time your Multi will spend in Bulk mode, and less time in Absorption. Just don't exceed your Battery manufacturers recommendation for Bulk charging voltage. If you tune the absorb voltage just right , you should be able to get the Multi to stay in Bulk up to 80 or 90% SOC, and the minimum settable Hour limit on Absorb will then get you to 100%.
(14.0V is a good place to start) - See your battery specs

Also very important for lithium's is to set your LOW battery Cut-Out Voltages and LOW SOC cut-out,

if you are NOT using DVCC to interact with a BMS you can enable it, disable voltage control and sharing, and then access the charge current limit via Node red, it will accept a 0 value. This stops the charger whilst leaving bypass/assist available and unaffected. Note that The AC current limit is applied first so a high charge current setting will not be met if yu are AC limmited.

That said, see previous posts because I agree, you probably dont need/want to do this anyway at least not for your stated reason.

I know this DVCC trick works because I have two Multis with one feeding the other and I manage what, if any, charge is shunted forward.